It is commonly used in classrooms to demonstrate an exothermic reaction.
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Another important thing to note is that the reaction is exothermic, meaning that the foam will be hot.
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To explain away the absence of audio or visual evidence of typical demolition charges, AE911Truth argues that the buildings were brought down by nano-thermite, a material with a highly exothermic reaction which hardly exists outside of advanced physics journals.
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As proof of its claims, it cites puffs of smoke emanating from the collapsing building (demolition squibs), large clouds of dust and ash (proof of highly energetic explosive material), and the presence of supposedly molten material in the debris pile (nano-thermite's persistent exothermic reaction).
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Chemical exothermic reactions are generally more spontaneous than their counterparts, endothermic reactions. In a thermochemical reaction that is exothermic, the heat may be listed among the products of the reaction.
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The thermite reaction is famously exothermic. The reduction of iron(III) oxide by aluminium releases sufficient heat to yield molten iron. An exothermic reaction is a "reaction for which the overall standard enthalpy change ΔH⚬ is negative." Exothermic reactions usually release heat and entail the replacement of weak bonds with stronger ones.
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Exothermic reactions release heat, and ones that are highly exothermic can cause safety concerns. Semibatch reactors allow for slow addition of reactants in order to control the heat released and thus, temperature, in the reactor.
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It is used extensively by the electrical utilities and telecommunications industries (exothermic welded connections).
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Formation of an intermetallic compound can be a strongly exothermic reaction, usable as an initiator.
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Thermite welding was a step forward for joining rails A thermite weld in progress. Exothermic welding, also known as exothermic bonding, thermite welding (TW), and thermit welding, is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composition to heat the metal, and requires no external source of heat or current. The chemical reaction that produces the heat is an aluminothermic reaction between aluminium powder and a metal oxide.
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Examples are numerous: combustion, the thermite reaction, combining strong acids and bases, polymerizations. As an example in everyday life, hand warmers make use of the oxidation of iron to achieve an exothermic reaction: :4Fe \+ 3O2 → 2Fe2O3 ΔH⚬ = - 1648 kJ/mol A particularly important class of exothermic reactions is combustion of a hydrocarbon fuel, e.g. the burning of natural gas: :CH4 + 2O2 -> CO2 + 2H2O ΔH⚬ = - 890 kJ/mol Video of an exothermic reaction. Ethanol vapor is ignited inside a bottle, causing combustion.
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Neutralization is an exothermic reaction. The standard enthalpy change for the reaction H+ \+ OH− → H2O is −57.30 kJ/mol.
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In general, reactions involving NBS are exothermic. Therefore, extra precautions should be taken when used on a large scale.
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The oxidation of pyrite is highly exothermic, allowing the autoclave to operate at this temperature without an external heat source.
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In the presence of pure hydrogen, dihydridochromim readily converts to bis(dihydrogen)dihydridochromium, CrH2(H2)2 in an exothermic reaction.
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Remote exothermic welding is a type of exothermic welding process for joining two electrical conductors from a distance. The process reduces the inherent risks associated with exothermic welding and is used in installations that require a welding operator to permanently join conductors from a safe distance from the superheated copper alloy. The process incorporates either an igniter for use with standard graphite molds or a consumable sealed drop-in weld metal cartridge, semi-permanent graphite crucible mold, and an ignition source that tethers to the cartridge with a cable that provides the safe remote ignition.
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However consider another example: in the contact process for the production of sulfuric acid, the second stage is a reversible reaction: :2SO2(g) + O2(g) ⇌ 2SO3(g) The forward reaction is exothermic and the reverse reaction is endothermic. Viewed by Le Chatelier's principle a larger amount of thermal energy in the system would favor the endothermic reverse reaction, as this would absorb the increased energy; in other words the equilibrium would shift to the reactants in order to remove the stress of added heat. For similar reasons, lower temperatures would favor the exothermic forward reaction, and produce more products. This works in this case, since due to loss of entropy the reaction becomes less exothermic as temperature increases; however reactions that become more exothermic as temperature increases would seem to violate this principle.
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The exothermic cross-linking reaction is initiated through a catalyst, usually an organic peroxide such as methyl ethyl ketone peroxide or benzoyl peroxide.
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The alkene ozonolysis reaction is extremely exothermic, releasing about of excess energy. Therefore, the Criegee intermediates are formed with a large amount of internal energy.
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Coade stone was superseded by products using naturally exothermic Portland cement as a binder, and appears to have been largely phased out by the 1840s.
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Methanesulfonyl chloride is highly toxic by inhalation, corrosive, and acts as a lachrymator. It reacts with nucleophilic reagents (including water) in a strongly exothermic manner.
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Charles Cadwell, was a professor at the Case School of Applied Science (now Case Western Reserve University), in Cleveland, Ohio. He further developed the exothermic welding system previously invented by Hans Goldschmidt in 1895; in 1938-1939 Cadwell developed a non-ferrous exothermic welding process using copper, today widely known as "Cadweld".Improvements and innovation in the exothermic welding procedure, Aplicaciones Tecnológicas, S.A. The original use of the process was to weld signal bonds to railroad tracks, which previously had to be done with "pins" knocked into holes drilled into the web of the rail. Later developments allows the rails themselves to be welded together.
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As their chemical reactions are energetic and exothermic, there is also a fire risk, as with respirators. Faulty SCSRs were implicated in the Sago Mine disaster.
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The variably hydrated phases of calcium sulfate (gypsum, bassanite and anhydrite) also exhibit a retrograde solubility for the same reason because their dissolution reactions are exothermic.
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The products of hydrolysis are mainly hydrofluoric acid and hydrochloric acid, usually released as acidic steam or vapor due to the highly exothermic nature of the reaction.
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The cyanide can then be oxidized by sodium or calcium hypochlorite to the less toxic cyanate ion. Note that deactivation is extremely exothermic and may be explosive.
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Chain branching is an additional positive feedback mechanism which may also cause temperature to skyrocket because of rapidly increasing reaction rate. Chemical reactions are either endothermic or exothermic, as expressed by their change in enthalpy. Many reactions are highly exothermic, so many industrial-scale and oil refinery processes have some level of risk of thermal runaway. These include hydrocracking, hydrogenation, alkylation (SN2), oxidation, metalation and nucleophilic aromatic substitution.
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It is an isomer of N-methylhydroxylamine and aminomethanol. It decomposes in an exothermic reaction (-56 kJ/mol) to methane and azanone unless stored as a hydrochloride salt.
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Oleylamine reacts with carboxylic acid to form its carboxylate salt through an exothermic reaction. Its carboxylate salt can further condensate into amides through the loss of one water molecule.
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At 120 °C, hydroxylammonium sulfate begins to decompose to sulfur trioxide, nitrous oxide, water, and ammonia: :2(NH3OH)2SO4 → 2SO3 \+ N2O + 2NH3 \+ 5H2O The reaction is exothermic above 138 °C, and is most exothermic at 177 °C.BASF hydroxylammonium sulfate product page Metals (especially copper, its alloys and its salts) catalyse the decomposition of hydroxylammonium sulfate. The instability of this compound is mainly due to the hydroxylammonium ion's weak nitrogen to oxygen single bond.
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Freezing is almost always an exothermic process, meaning that as liquid changes into solid, heat and pressure are released. This is often seen as counter-intuitive,What is an exothermic reaction? Scientific American, 1999 since the temperature of the material does not rise during freezing, except if the liquid were supercooled. But this can be understood since heat must be continually removed from the freezing liquid or the freezing process will stop.
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The reaction typically needs to be heated to initiate the process, however once started the Reimer-Tiemann Reaction can be highly exothermic, this combination makes it prone to thermal runaways.
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SOEC modules can operate in three different modes: thermoneutral, exothermic and endothermic. In exothermic mode, the stack temperature increases during operation due to heat accumulation, and this heat is used for inlet gas preheating. Therefore, an external heat source is not needed while the electrical energy consumption increases. In the endothermic stack operation mode, there is an increment in heat energy consumption and a reduction in electrical energy consumption and hydrogen production because the average current density also decreases.
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The process is exothermic and proceeds as a chain reaction initiated by the homolytic cleavage of molecular chlorine into chlorine radicals by ultraviolet radiation. Many chlorinated solvents are produced in this way.
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The term is often confused with exergonic reaction, which IUPAC defines as "... a reaction for which the overall standard Gibbs energy change ΔG⚬ is negative." A strongly exothermic reaction will usually also be exergonic because ΔH⚬ makes a major contribution to ΔG⚬. Most of the spectacular chemical reactions that are demonstrated in classrooms are exothermic and exergonic. The opposite is an endothermic reaction, which usually takes up heat and is driven by an entropy increase in the system.
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To use electron affinities properly, it is essential to keep track of sign. For any reaction that releases energy, the change ΔE in total energy has a negative value and the reaction is called an exothermic process. Electron capture for almost all non-noble gas atoms involves the release of energyChemical Principles the Quest for Insight, Peter Atkins and Loretta Jones, Freeman, New York, 2010 and thus are exothermic. The positive values that are listed in tables of Eea are amounts or magnitudes.
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Transport reactions are classified according to the thermodynamics of the reaction between the solid and the transporting agent. When the reaction is exothermic, then the solid of interest is transported from the cooler end (which can be quite hot) of the reactor to a hot end, where the equilibrium constant is less favorable and the crystals grow. The reaction of molybdenum dioxide with the transporting agent iodine is an exothermic process, thus the MoO2 migrates from the cooler end (700 °C) to the hotter end (900 °C): :MoO2 \+ I2 MoO2I2 ΔHrxn < 0 (exothermic) Using 10 milligrams of iodine for 4 grams of the solid, the process requires several days. Alternatively, when the reaction of the solid and the transport agent is endothermic, the solid is transported from a hot zone to a cooler one.
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The species in this genus are haemogregarines and infect exothermic vertebrates. They have erythrocytic gamogony, both erythrocytic and extra-erythrocytic merogony and cystogony. The definitive hosts are ixodid ticks. Sporogony occurs in two phases.
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Neutralizing acid spills with strong bases, such as sodium hydroxide or potassium hydroxide, can cause a violent exothermic reaction, and the base itself can cause just as much damage as the original acid spill.
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The compound can be prepared by the exothermic reaction of sucrose with acetic anhydride at about 145 °C, with sodium acetate as catalyst. The product can be purified by dissolution in ethanol and recrystallization.
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Dipropyl peroxydicarbonate (trade name Luperox 221) is an organic peroxide with a variety of industrial uses, particularly as an initiator of polymerization. Dipropyl peroxydicarbonate decomposes explosively at due to a self-accelerating exothermic decomposition.
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An absorption or release of nuclear energy occurs in nuclear reactions or radioactive decay; those that absorb energy are called endothermic reactions and those that release energy are exothermic reactions. Energy is consumed or liberated because of differences in the nuclear binding energy between the incoming and outgoing products of the nuclear transmutation. The best-known classes of exothermic nuclear transmutations are fission and fusion. Nuclear energy may be liberated by atomic fission, when heavy atomic nuclei (like uranium and plutonium) are broken apart into lighter nuclei.
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Carbene cyclopropanation Carbenes add to double bonds to form cyclopropanes. A concerted mechanism is available for singlet carbenes. Triplet carbenes do not retain stereochemistry in the product molecule. Addition reactions are commonly very fast and exothermic.
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When these two components are mixed, the reaction is exothermic as ion-dipole intermolecular forces of attraction are formed between the resulting ions (H3O+ and Cl–) and the polar water molecules so that ΔHmix is negative.
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The preparation of potassium methoxide can be achieved on the laboratory scale by the (strongly exothermic) reaction of metallic potassium and methanol upon the release of equimolar amounts of hydrogen. Kaliummethanolat aus Kalium und Methanol The reaction of metal hydrides (potassium hydride) with methanol forming potassium methoxide is also possible but less important. Kaliummethanolat aus Kaliumhydrid und Methanol The exothermic reaction of potassium hydroxide with methanol leads in an equilibrium reaction to potassium methanolate and water (avoiding formation of highly inflammable hydrogen gas). In a continuous process the formed water must be removed permanently.
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Triflic acid is one of the strongest acids. Contact with skin causes severe burns with delayed tissue destruction. On inhalation it causes fatal spasms, inflammation and edema. Addition of triflic acid to polar solvents can be dangerously exothermic.
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The compound was first prepared by thermolysis of the ammonium salt [C4H7NMe3]OH. Cyclobutene thermally isomerizes to 1,3-butadiene. This strongly exothermic reaction reflects the dominance of ring strain. In contrast, the corresponding equilibrium for hexafluorocyclobutene disfavors hexafluorobutadiene.
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Ethyl cyanoacrylate is prepared by the condensation of formaldehyde with ethyl cyanoacetate: : + → + This exothermic reaction affords the polymer, which is subsequently sintered, thermally "cracked" to give the monomer. Alternatively, it can be prepared by the ethoxycarbonylation of cyanoacetylene.
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The Romans made concrete by mixing lime and volcanic ash to create a pozzolanic reaction. If this was mixed with volcanic tuff and placed under seawater, the seawater hydrated the lime in an exothermic reaction that solidified the mixture.
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Contrary to some earlier reports, ethenium was found to be largely unreactive towards neutral methane at ambient temperature and low pressure (on the order of 1 mmHg), even though the reaction yielding sec- and is believed to be exothermic.
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In addition, zircaloy can react with uranium dioxide to form zirconium dioxide and uranium metal. This exothermic reaction together with the reaction of boron carbide with stainless steel can release additional heat energy, thus contributing to the overheating of a reactor.
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The excess of EDTA is back- titrated with a suitable metal ion such as Mn2+ or Cu2+. At the endpoint, the first excess of metal ion catalyzes a strongly exothermic reaction between a polyhdric phenol (such as resorcinol) and hydrogen peroxide.
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Potassium reacts with oxygen, water, and carbon dioxide components in air. With oxygen it forms potassium peroxide. With water potassium forms potassium hydroxide. The reaction of potassium with water can be violently exothermic, especially since the coproduced hydrogen gas can ignite.
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Grounding connectors Connectors for earthing installation are a means of communication between the various components of the earthing and lightning protection installations (earthing rods, earthing conductors, current leads, busbars, etc.). For high voltage installations, exothermic welding is used for underground connections.
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Strong oxidizing acids may cause a vigorous reaction that is sufficiently exothermic to ignite the reaction products. Heat is also generated by the interaction of esters with caustic solutions. Flammable hydrogen is generated by mixing esters with alkali metals and hydrides.
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As of 2012 QuikClot devices are impregnated with kaolin, an inorganic mineral that accelerates the body's natural clotting ability, and produces no exothermic reaction. The product consists of a non-woven gauze coated in kaolin which can be applied to the region of trauma to promote clotting without an exothermic reaction. Originally sold as QuikClot Combat Gauze, the product now has a variety of packaging options available for military, law enforcement, emergency medical responders public access and hospital use. Consumer versions of the product, which use kaolin formulation, are also available at a variety of retailers.
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The element iron can combine with chlorine at high temperatures in a strong exothermic reaction, creating a chlorine-iron fire. Chlorine-iron fires are a risk in chemical process plants, where much of the pipework that carries chlorine gas is made of steel.
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Sodium phosphide is highly dangerous releasing toxic phosphine upon hydrolysis, a process that is so exothermic that fires result. The USDOT has forbidden the transportation of Na3P on passenger aircraft, cargo only aircraft, and trains due to the potential fire and toxic hazards.
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The temperature of the reaction can be moderated by the addition of inert salt that absorbs heat in the process of melting or evaporation, such as sodium chloride, or by adding "chemical oven"—a highly exothermic mixture—to decrease the ratio of cooling .
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When the wood is dry its temperature rises, and at about 270°C, it begins to spontaneously decompose. This is the well known exothermic reaction which takes place in charcoal burning. At this stage evolution of the by-products of wood carbonization starts.
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These fumes are then oxidized in reburn tunnels where oxygen is injected progressively. The exothermic oxidation reaction maintains the temperature of the reburn tunnels. This system allows lower temperatures to be employed in the incinerator section, where the solids are volumetrically reduced.
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The chemical reaction is exothermic and the exterior temperature of the canister will reach . It will produce oxygen for 12 to 22 minutes. The two-mask generator is approximately in diameter and long. The three-mask generator is approximately in diameter and long.
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Rags used for Danish oil, like those used for linseed oil, have some potential risk of spontaneous combustion and starting fires from exothermic oxidation, so it is best to dry rags flat before disposing of them, or else soak them in water.
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The reaction between 2,4,5-trichlorophenol and formaldehyde is exothermic. If the reaction occurs without adequate cooling, TCDD is produced in significant quantities as a byproduct and contaminant. The Seveso disaster and the Times Beach, Missouri contamination incident exemplify the industrial hazards of hexachlorophene production.
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Monoammonium phosphate is industrially prepared by the exothermic reaction of phosphoric acid and ammonia in the correct proportions:Martin Bäckman, Martin Gunnarsson, Linnea Kollberg, Martin Müller, and Simon Tallvod (2016): "Production of Monoammonium Phosphate at Yara AB ". Technical Report, Lund University. : + → Crystalline MAP then precipitates.
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University of Cambridge, Material Science and Metallurgy. www.msm.cam.ac.uk/phase-trans/2002/Thermal1.pdf This differential temperature is then plotted against time, or against temperature (DTA curve, or thermogram). Changes in the sample, either exothermic or endothermic, can be detected relative to the inert reference.
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Dissolution by most gases is exothermic. That is, when a gas dissolves in a liquid solvent, energy is released as heat, warming both the system (i.e. the solution) and the surroundings. The temperature of the solution eventually decreases to match that of the surroundings.
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Solid reactant welding uses reactions between elements and compounds. Certain compounds when mixed create an exothermic chemical reaction, meaning they give off heat. A very common reaction uses thermite, a combination of a metal oxide (rust) and aluminum. This reaction produces heat over 4000 °F.
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Exothermic welding is usually used for welding copper conductors but is suitable for welding a wide range of metals, including stainless steel, cast iron, common steel, brass, bronze, and Monel. It is especially useful for joining dissimilar metals. The process is marketed under a variety of names such as Harger ULTRASHOT, American Rail Weld, ERICO CADWELD, Quikweld, Tectoweld, Ultraweld, Techweld, TerraWeld, Thermoweld, Ardo Weld, AmiableWeld, AIWeld, FurseWeld, CADWELL TVT and Kumwell. Because of the good electrical conductivity and high stability in the face of short-circuit pulses, exothermic welds are one of the options specified by §250.7 of the United States National Electrical Code for grounding conductors and bonding jumpers.
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The first reaction, between incandescent coke and steam, is strongly endothermic, producing carbon monoxide (CO), and hydrogen (water gas in older terminology). When the coke bed has cooled to a temperature at which the endothermic reaction can no longer proceed, the steam is then replaced by a blast of air. The second and third reactions then take place, producing an exothermic reaction—forming initially carbon dioxide and raising the temperature of the coke bed—followed by the second endothermic reaction, in which the latter is converted to carbon monoxide, CO. The overall reaction is exothermic, forming "producer gas" (older terminology). Steam can then be re-injected, then air etc.
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The HDDA reaction is often thermodynamically favorable (exothermic), but can have a significant kinetic barrier to reaction (high activation energy). Calculations have suggested that the formation of unsubstituted o-benzyne (from butadiyne and acetylene, above) has an activation energy of 36 kcal mol−1, but is thermodynamically favorable, estimated to be exothermic by -51 kcal mol−1. As a result of higher activation energy, some HDDA reactions require heating to elevated temperatures (>100 ⁰C) in order to initiate. Furthermore, the benzyne trapping step is also thermodynamically favourable, calculated to be an additional -73 kcal mol−1 for trapping of an ester-substituted o-benzyne with tert-butanol.
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An aluminothermic reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake. Aluminothermic reactions are exothermic chemical reactions using aluminium as the reducing agent at high temperature. The process is industrially useful for production of alloys of iron.
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New Zealand Engineering News. magnetic pulse welding,Stephan Kallee et al. (2010) Industrialisation of Electromagnetic Pulse Technology (EMPT) in India 38th Anniversary Issue of PURCHASE India. co-extrusion welding, cold welding, diffusion bonding, exothermic welding, high frequency welding, hot pressure welding, induction welding, and roll bonding.
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Volume combustion synthesis (VCS) is method of chemical synthesis in which the reactants are heated uniformly in a controlled manner until a reaction ignites throughout the volume of the reaction chamber. The VCS mode is typically used for weakly exothermic reactions that require preheating prior to ignition.
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Smaller quantities can be prepared by the partial oxidation of ethanol in an exothermic reaction. This process typically is conducted over a silver catalyst at about 500–650 °C. : CH3CH2OH + O2 → CH3CHO + H2O This method is one of the oldest routes for the industrial preparation of acetaldehyde.
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Self-propagating high-temperature synthesis (SHS) is a method for producing both inorganic and organic compounds by exothermic combustion reactions in solids of different nature."Concise Encyclopedia of Self-Propagating High- Temperature Synthesis. History, Theory, Technology, and Products". 1st Ed., Editors: I.Borovinskaya, A.Gromov, E.Levashov et al.
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Nitroethane is produced industrially by treating propane with nitric acid at 350–450 °C. This exothermic reaction produces four industrially significant nitroalkanes: nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane. The reaction involves free radicals, such as CH3CH2CH2O., which arise via homolysis of the corresponding nitrite ester.
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Potassium hydroxide is usually sold as translucent pellets, which become tacky in air because KOH is hygroscopic. Consequently, KOH typically contains varying amounts of water (as well as carbonates - see below). Its dissolution in water is strongly exothermic. Concentrated aqueous solutions are sometimes called potassium lyes.
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This polymerisation is undesirable, as it can foul the fractionating tower, it is also typically exothermic which can lead to a runaway reaction and potential explosion if left unchecked. Once initiated polymerisation is typically radical in mechanism and as such many polymerisation inhibitors act as radical scavengers.
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The brick-red color of unreacted chromium trioxide (chromic anhydride). The Sarett reagent was originally prepared in 1953 by addition of chromium trioxide to pyridine. The pyridine must be cooled because the reaction is dangerously exothermic. Slowly, the brick-red CrO3 transform into the bis(pyridine) adduct.
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A large compost pile can spontaneously combust if not properly managed. Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, autoignition.
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Flames of charcoal A flame (from Latin flamma) is the visible, gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone. Very hot flames are hot enough to have ionized gaseous components of sufficient density to be considered plasma..
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Orthophosphate ion can be conveniently thermometrically titrated with magnesium ions in the presence of ammonium ion. An aliquot of sample is buffered to approximately pH10 with an NH3/NH4Cl solution. The reaction: : Mg2+ \+ NH4+ \+ PO43− ↔ MgNH4PO4↓ Is exothermic. CV’s of under 0.1 have been achieved in test applications.
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Mixing the solution is extremely exothermic. If the solution is made rapidly, it will instantly boil, releasing large amounts of corrosive fumes. Even when made with care, the resultant heat can bring solution temperatures above 100 °C. It must be allowed to cool reasonably before it is used.
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Lithium chloride is produced by treatment of lithium carbonate with hydrochloric acid. It can in principle also be generated by the highly exothermic reaction of lithium metal with either chlorine or anhydrous hydrogen chloride gas. Anhydrous LiCl is prepared from the hydrate by heating with a stream of hydrogen chloride.
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It is the preferred method of bonding, and indeed it is the only acceptable means of bonding copper to galvanized cable. The NEC does not require such exothermically welded connections to be listed or labelled, but some engineering specifications require that completed exothermic welds be examined using X-ray equipment.
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Thermometric titrations of silver nitrate with halides and cyanide are all possible. The reaction of silver nitrate with chloride is strongly exothermic. For instance, the reaction enthalpy of Ag+ with Cl− is a high −61.2 kJ/mol. This permits convenient determination of chloride with commonly available standard 0.1 mol/L AgNO3.
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From the storage hoppers, the green beans are conveyed to the roaster. Initially, the process is endothermic (absorbing heat), but at around it becomes exothermic (giving off heat).Raemy A, Lambelet P. A calorimetric study of self-heating in coffee and chicory. Int J Food Sci & Tech, 1982;17(4):451–460.
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Nitrogen-containing explosophores (groups I, II and II below) are particularly strong because in addition to providing oxygen they react to form molecular nitrogen, which is a very stable molecule, and thus the overall reaction is strongly exothermic. The gas formed also expands, causing the shock wave which is observed.
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The tetrachloride is obtained upon dissolving the dioxide in hydrochloric acid; to prevent the exothermic decomposition, it is kept under concentrated sulfuric acid. The tetrabromide may not, and the tetraiodide definitely does not exist. The diastatide has also been prepared. The metal is not attacked by sulfuric or hydrochloric acids.
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A highly exothermic reaction combusts magnesium in an oxidation–reduction reaction with carbon dioxide, producing a variety of carbon nanoparticles including graphene and fullerenes. The carbon dioxide reactant may be either solid (dry-ice) or gaseous. The products of this reaction are carbon and magnesium oxide. was issued for this process.
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To absorb hydrogen, the dehydrated form of LOHC (an unsaturated, mostly aromatic compound) reacts with the hydrogen in a hydrogenation reaction. The hydrogenation is an exothermic reaction and is carried out at elevated pressures (approx. 30-50 bar) and temperatures of approx. 150-200°C in the presence of a catalyst.
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TNT explosive charge during Operation Sailor Hat. The passing blast-wave left behind a white water surface. A white condensation cloud is visible overhead. Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it.
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The manganese can be recovered by the Weldon process. Small amounts of chlorine gas can be made in the laboratory by putting concentrated hydrochloric acid in a flask with a side arm and rubber tubing attached. Manganese dioxide is then added and the flask stoppered. The reaction is not greatly exothermic.
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Other types of modern perms include exothermic perms, which are self timing and self heating; and neutral, or low pH, thioglycolate free perms. Digital perms were introduced in the 21st century and in use especially in modern Asian cultures. The process was patented and invented by a Japanese company, Paimore Ltd.
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2D silicene is not fully planar, apparently featuring chair-like puckering distortions in the rings. This leads to ordered surface ripples. Hydrogenation of silicenes to silicanes is exothermic. This led to the prediction that the process of conversion of silicene to silicane (hydrogenated silicene) is a candidate for hydrogen storage.
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The air is recycled through the scrubber, which will heat it slightly through the exothermic chemical reaction which removes carbon dioxide. The helmet is rigidly connected to the torso of the suit, which limits the field of vision. this can be partly compensated by using a nearly hemispherical dome viewport.
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In addition, there was little H+ at any pressure. These data suggested the proton exchange formation pathway discussed below. In 1961, Martin et al. first suggested that may be present in interstellar space given the large amount of hydrogen in interstellar space and its reaction pathway was exothermic (~1.5 eV).
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Reduction of alkyl halide with metallic lithium can afford simple alkyl and aryl organolithium reagents. Industrial preparation of organolithium reagents is achieved using this method by treating the alkyl chloride with metal lithium containing 0.5-2% sodium. The conversion is highly exothermic. The sodium initiates the radical pathway and increases the rate.
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Dissociation is an endothermic process, hence reducing the amount of energy released in a detonation or the maximum amount of work that can be obtained from the FJ cycle. Exothermic reactions are encouraged when increasing the initial pressure of the system, hence, increasing the amount of work generated during the FJ cycle.
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This reaction is exothermic and releases sufficient heat to ignite the resulting hydrogen in the presence of oxygen. Finely powdered potassium ignites in air at room temperature. The bulk metal ignites in air if heated. Because its density is 0.89g/cm3, burning potassium floats in water that exposes it to atmospheric oxygen.
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Most solids will adhere on contact to some extent. However, oxidation films, lubricants and contaminants naturally occurring generally suppress adhesion,Stachowiak, G. W., and A. W. Batchelor (2005). Engineering Tribology. Burlington, Elsevier Butterworth-Heinemann and spontaneous exothermic chemical reactions between surfaces generally produce a substance with low energy status in the absorbed species.
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Chlorination is generally highly exothermic. Both saturated and unsaturated compounds react directly with chlorine, the former usually requiring UV light to initiate homolysis of chlorine. Chlorination is conducted on a large scale industrially; major processes include routes to 1,2-dichloroethane (a precursor to PVC), as well as various chlorinated ethanes, as solvents.
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The conversion is highly exothermic. Coordination polymerization is the most pervasive technology, which means that metal chlorides or metal oxides are used. The most common catalysts consist of titanium(III) chloride, the so-called Ziegler–Natta catalysts. Another common catalyst is the Phillips catalyst, prepared by depositing chromium(VI) oxide on silica.
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The reaction is exothermic but slow. To recover the heat produced by the reaction to produce electricity, a large volume of olivine must be thermally well-isolated. The end-products of the reaction are silicon dioxide, magnesium carbonate, and small amounts of iron oxide. Olivine is used as a substitute for dolomite in steel works.
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As tetramethylammonium nitratoborate is heated it has some sort of transition between 51 and 62 °C. It decomposes above 75 °C producing gas. Above 112 °C it is exothermic, and a solid is left if it is heated to 160 °C. Tetramethylammonium nitratoborate is insoluble in cold water but slightly soluble in hot water.
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A frigorific mixture may be used to obtain a liquid medium that has a reproducible temperature below ambient temperature. Such mixtures were used to calibrate thermometers. In chemistry a cooling bath may be used to control the temperature of a strongly exothermic reaction. A frigorific mixture may be used as an alternative to mechanical refrigeration.
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The energy released by solvation of the ammonium ions and nitrate ions is less than the energy absorbed in breaking up the ammonium nitrate ionic lattice and the attractions between water molecules. Dissolving potassium hydroxide is exothermic, as more energy is released during solvation than is used in breaking up the solute and solvent.
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The blended powder is then pressed into a pellet and placed under an inert atmosphere of argon. The sample is then heated. A heated wire, a spark, a laser, or an oven may provide the heat. The exothermic reaction is initiated, and the resulting heat propagates the reaction throughout the rest of the sample.
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Henri Moissan and Lebeau recorded the preparation of nitryl fluoride in 1905 by the fluorination of nitrogen dioxide. This reaction is highly exothermic, which leads to contaminated products. The simplest method avoids fluorine gas but uses cobalt(III) fluoride: :NO2 \+ CoF3 → NO2F + CoF2 The CoF2 can be regenerated to CoF3. Other methods have been described.
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At the von Neumann spike point the explosive still remains unreacted. The spike marks the onset of the zone of exothermic chemical reaction, which finishes at the Chapman-Jouguet state. After that, the detonation products expand backward. In the reference frame in which the shock is stationary, the flow following the shock is subsonic.
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As is common for reactions involving solids and solution, the formation of Grignard reagents is often subject to an induction period. During this stage, the passivating oxide on the magnesium is removed. After this induction period, the reactions can be highly exothermic. This exothermicity must be considered when a reaction is scaled-up from laboratory to production plant.
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Chlorosulfuric acid (CSA) is a heavy, strongly acidic liquid. When dispensed in air, it readily absorbs moisture and forms dense white fog of hydrochloric acid and sulfuric acid. In moderate concentrations it is highly irritating to eyes, nose, and skin. When chlorosulfuric acid comes in contact with water, a strong exothermic reaction scatters the corrosive mixture in all directions.
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Fluorine can act both as an electrophilic and atomic source of fluorine. The weak F—F bond strength () allows for homolytic cleavage. The reaction of F2 with organic compounds is, however, highly exothermic and can lead to non- selective fluorinations and C—C cleavage, as well as explosions. Only a few selective radical fluorination methods have been reported.
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Xenon tetrafluoride is a chemical compound with chemical formula . It was the first discovered binary compound of a noble gas. It is produced by the chemical reaction of xenon with fluorine, , according to the chemical equation: : Xe + 2 → This reaction is exothermic, releasing an energy of 251 kJ/mol. Xenon tetrafluoride is a colorless crystalline substance.
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The hardening of the concrete is called hydration. The reaction is exothermic (gives off heat). Concrete increases in strength continually from the day it is cast. Assuming it is not cast under water or in constantly 100% relative humidity, it shrinks over time as it dries out, and it deforms over time due to a phenomenon called creep.
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Solving for the standard of enthalpy of formation, :ΔfH⦵(CH4) = [ΔfH⦵(CO2) + 2 ΔfH⦵(H2O)] − ΔcombH⦵(CH4). The value of ΔfH⦵(CH4) is determined to be −74.8 kJ/mol. The negative sign shows that the reaction, if it were to proceed, would be exothermic; that is, methane is enthalpically more stable than hydrogen gas and carbon.
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At further heating to phase II can be handled safely in an ambient environment. The metal reacts with the silica gel in an exothermic reaction in which Na4Si4 nanoparticles are formed. The powder reacts with water to form hydrogen. Compounds such as biphenyl and naphthalene are reduced by the powder and form highly coloured radical anions.
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If the reactions occurring during crosslinking are exothermic, the crosslinking rate can be related to the heat released during the process. Higher is the number of bonds created, higher is the heat released in the reaction. At the end of the reaction, no more heat will be released. To measure the heat flow differential scanning calorimetry can be used.
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A special case of chain-growth polymerization leads to living polymerization. Ziegler–Natta polymerization allows considerable control of polymer branching. Polymerization of ethylene Diverse methods are employed to manipulate the initiation, propagation, and termination rates during chain polymerization. A related issue is temperature control, also called heat management, during these reactions, which are often highly exothermic.
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"Combustion" refers to burning fuel with an oxidizer, to supply the heat. Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal or exothermic reactions not involving combustion; they are not then strictly classed as external combustion engines, but as external thermal engines.
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Self-heating field rations for up to 18 soldiers Self-heating food packaging is active packaging with the ability to heat food contents without external heat sources or power. Packets typically use an exothermic chemical reaction. Packets can also be self-cooling. These packages are useful for military operations, during natural disasters, or whenever conventional cooking is not available.
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Lithium nitride has been investigated as a storage medium for hydrogen gas, as the reaction is reversible at 270 °C. Up to 11.5% by weight absorption of hydrogen has been achieved. Reacting lithium nitride with carbon dioxide results in amorphous carbon nitride (C3N4), a semiconductor, and lithium cyanamide (Li2CN2), a precursor to fertilizers, in an exothermic reaction.
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This light that is released can be absorbed by other molecules in solution to give rise to molecular translations and rotations, which gives rise to the classical understanding of heat. In an exothermic reaction, the energy needed to start the reaction is less than the energy that is subsequently released, so there is a net release of energy.
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5b00407 chlorate, or perchlorate; ozonides are a promising group of oxygen sources. The generators are usually ignited by a firing pin, and the chemical reaction is usually exothermic, making the generator a potential fire hazard. Potassium superoxide was used as an oxygen source on early manned missions of the Soviet space program, for firefighters, and for mine rescue.
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The standard first aid measures for alkali spills on the skin is, as for other corrosives, irrigation with large quantities of water. Washing is continued for at least ten to fifteen minutes. Moreover, dissolution of sodium hydroxide is highly exothermic, and the resulting heat may cause heat burns or ignite flammables. It also produces heat when reacted with acids.
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Fig 3. Sankey diagram of energy fluxes in a reversible CLC system.Fig 3 illustrates the energy exchanges in a CLC system graphically and shows a Sankey diagram of the energy fluxes occurring in a reversible CLC based engine. Studying Fig 1, a heat engine is arranged to receive heat at high temperatures from the exothermic oxidation reaction.
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Many chemicals may react adversely when combined. It is recommended that incompatible chemicals be stored in separate areas of the lab. Acids should be separated from alkalis, metals, cyanides, sulfides, azides, phosphides, and oxidizers. The reason being, when combined acids with these type of compounds, violent exothermic reaction can occur possibly causing flammable gas, and in some cases explosions.
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No. 19,4 (1976) which maintain the fireball and can extend its duration to between 10 and 50 ms as exothermic recombination reactions occur.May L.Chan (2001) Advanced Thermobaric Explosive Compositions. Further damage can result as the gases cool and pressure drops sharply, leading to a partial vacuum. This rarefaction effect has given rise to the misnomer "vacuum bomb".
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N-Methylhydroxylamine or methylhydroxylamine is a hydroxylamine derivative with a methyl group replacing one of the hydrogens of the amino group. It is an isomer of methoxyamine and aminomethanol. It decomposes in an exothermic reaction (-63 kJ/mol) into methane and azanone unless stored as a hydrochloride salt. The compound is commercially available as its hydrochloride salt.
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Symmetrical 1,3,5-triazines are prepared by trimerization of certain nitriles such as cyanogen chloride or cyanimide. Cyanogen chloride and cyanogen bromide each trimerize at elevated temperatures over a carbon catalyst. The chloride gives cyanuric chloride: :300px The bromide has an extended shelflife when refrigerated. Like the chloride, it undergoes ab exothermic trimerisation to form cyanuric bromide.
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Its strong dipole and high abundance make it easily detectable by radioastronomy. can also react with atomic oxygen to form OH+ and H2. : + O → OH+ \+ H2 OH+ then usually reacts with more H2 to create further hydrogenated molecules. :OH+ \+ H2 → + H : + H2 → + H At this point, the reaction between and H2 is no longer exothermic in interstellar clouds.
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Nylon 1,6 is synthesized from adiponitrile, formaldehyde, and water via acid catalysis. Adiponitrile and formaldehyde (aqueous, paraformaldehyde, or trioxane) are combined with an acid (typically sulfuric acid) in a reactor. The reaction can be performed at room temperature. However, the reaction is exothermic, and especially at high ratios of formaldehyde to adiponitrile, cooling may be required.
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This solution is capable of cooling to room temperature without forming crystals. By pressing on a metal disc within the heating pad, a nucleation center is formed, causing the solution to crystallize back into solid sodium acetate trihydrate. The bond-forming process of crystallization is exothermic. The latent heat of fusion is about 264–289 kJ/kg.
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Then H2 \+ H2+ → H3+ \+ H. The reaction is exothermic with an energy of 1.7eV, so the ions produced are hot with much vibrational energy. These can cool down via collisions with cooler gas if the pressure is high enough. This is significant because strongly vibrating ions produce strongly vibrating neutral molecules when neutralised according to the Franck–Condon principle.
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The negative value means that heat is produced and the system is exothermic. Endothermic: A + B + Heat → C, ΔH > 0 Exothermic: A + B → C + Heat, ΔH < 0 Since enthalpy is a state function, the ΔH given for a particular reaction is only true for that exact reaction. Physical states (of reactants or products) matter, as do molar concentrations. This matter of ΔH being dependent on physical state and molar concentration means that thermochemical equations must be stoichiometrically correct. If one agent of the equation is changed through multiplication, then all agents must be proportionally changed, including ΔH. (See Manipulating Thermochemical Equations, below.) Thermochemical equation’s multiplicative property is largely due to the First Law of Thermodynamics, which says that energy can be neither created nor destroyed, a concept commonly known as the conservation of energy.
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Useful reactions of this diene are cycloadditions, such as the Diels-Alder reaction.Sanjeeva Rao Guppi, George A. O'Doherty, "1,3-Cyclohexadiene" Encyclopedia of Reagents for Organic Synthesis, 2008 John Wiley & Sons. Conversion of cyclohexa-1,3-diene to benzene + hydrogen is exothermic by about 25 kJ/mol in the gas phase.US National Institute of Standards and Technology, NIST Chemistry WebBook 1,3-Cyclohexadiene BenzeneJ. Sherman The heats of hydrogenation of unsaturated hydrocarbons Journal of the American Oil Chemists' Society; Volume 16, Number 2 / February, 1939 :cyclohexane → cyclohexa-1,3-diene + 2 H2 (ΔH = +231.5 kJ/mol; endothermic) :cyclohexane → benzene + 3 H2 (ΔH = +205 kJ/mol; endothermic) :cyclohexa-1,3-diene → benzene + H2 (ΔH = -26.5 kJ/mol; exothermic) Compared with its isomer cyclohexa-1,4-diene, cyclohexa-1,3-diene is about 1.6 kJ/mol more stable.
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This type of reaction often exhibits an induction period as well. The reactions to form Grignard reagents are notorious for having induction periods. This is usually due to two reasons: Firstly, the thin film of oxide on the magnesium reagent must be removed before the bulk magnesium can react. Secondly, Grignard reactions, while exothermic, are typically conducted at low temperature for better selectivity.
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Angel Island chuckwallas are diurnal animals, and as they are exothermic, spend much of their mornings and winter days basking. These lizards are well adapted to desert conditions; they are active at temperatures up to 102 °F (39 °C). Mating occurs from April to July, with five to 16 eggs laid between June and August. The eggs hatch in late September.
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Recalescence is an increase in temperature that occurs while cooling metal when a change in structure with an increase in entropy occurs. The heat responsible for the change in temperature is due to the change in entropy. When a structure transformation occurs the Gibbs free energy of both structures are more or less the same. Therefore, the process will be exothermic.
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Usually for acyclic systems trans isomers are more stable than cis isomers. This is typically due to the increased unfavorable steric interaction of the substituents in the cis isomer. Therefore, trans isomers have a less- exothermic heat of combustion, indicating higher thermochemical stability. In the Benson heat of formation group additivity dataset, cis isomers suffer a 1.10 kcal/mol stability penalty.
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Her research includes Optimal Crew Selection for Long-Duration Spaceflight focusing on gender, culture, and personality characteristics, in which she contributed academic papers and presented her work at the Human Performance in Extreme Environments (HPEE) Conference, Spacecraft Propulsion Technologies, and Exothermic Welding in a Reduced Gravity Environment. Amber is a published author that has contributed to advancements in the Physiology field.
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The energy required to sustain the high temperature pyrometallurgical processes may derive from the exothermic nature of the chemical reactions taking place. Typically, these reactions are oxidation, e.g. of sulfide to sulfur dioxide . Often, however, energy must be added to the process by combustion of fuel or, in the case of some smelting processes, by the direct application of electrical energy.
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Epoxy putty refers to a group of room-temperature-hardening substances used as space-filling adhesives. Exact compositions vary according to manufacturer and application. They are stored until use as two components of clay-like consistency. Kneading the two components into each other creates an exothermic chemical reaction that activates the substance for use by catalyzing an epoxide polymerisation reaction.
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Taum Sauk (Missouri) pumped storage facility in late November 2009. After the original reservoir failed, the new reservoir was made of roller-compacted concrete. Due to cement's exothermic chemical reaction while setting up, large concrete structures such as dams, navigation locks, large mat foundations, and large breakwaters generate excessive heat during hydration and associated expansion. To mitigate these effects, post- coolingMass Concrete .
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Spontaneous combustion is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self-heating which rapidly accelerates to high temperatures) and finally, ignition. For example, phosphorus self-ignites at room temperature without the application of heat. Organic materials undergoing bacterial composting can generate enough heat to reach the point of combustion.
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The mountain ridge, to which the Hohe Kanzel also belongs, is made of hard, weathered, but also cracked and permeable quartzite rock. Its layers are set steeply and often vertically. This yellowish-white, sometimes cherry-red-streaked Taunus quartzite arose from sandy sea depositions. Through the mountain range's compression and the attendant exothermic reaction, the original sedimentary stone changed into metamorphic quartzite.
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It is for this same reason that carbon almost always forms four bonds. Its ground state valence configuration is 2s2 2p2, half filled. However, the activation energy to go from half filled to fully filled p orbitals is so small it is negligible, and as such carbon forms them almost instantaneously. Meanwhile, the process releases a significant amount of energy (exothermic).
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It has been suggested that eager would be a more intuitive term in this context. More generally, the terms exergonic and endergonic relate to the free energy change in any process, not just chemical reactions. By contrast, the terms exothermic and endothermic relate to an enthalpy change in a closed system during a process, usually associated with the exchange of heat.
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Copper sulfate is commonly included in children's chemistry sets. It is often used to grow crystals in schools and in copper plating experiments, despite its toxicity. Copper sulfate is often used to demonstrate an exothermic reaction, in which steel wool or magnesium ribbon is placed in an aqueous solution of CuSO4. It is used to demonstrate the principle of mineral hydration.
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MMT is manufactured by reduction of bis(methylcyclopentadienyl) manganese using triethylaluminium. The reduction is conducted under an atmosphere of carbon monoxide. The reaction is exothermic, and without proper cooling, can lead to catastrophic thermal runaway. MMT is a so-called half-sandwich compound, or more specifically a piano-stool complex (since the three CO ligands are like the legs of a piano stool).
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Combined reforming is a combination of partial oxidation and steam reforming and is the last reaction that is used for hydrogen production. The general equation is given below: and are the stoichiometric coefficients for steam reforming and partial oxidation, respectively. The reaction can be both endothermic and exothermic determined by the conditions, and combine both the advantages of steam reforming and partial oxidation.
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This exits the furnace and passes through cooling drums before being milled, screened and sent to product storage facilities. The process involves intermediate formation of sodium bisulfate, an exothermic reaction that occur at room temperature: :NaCl + H2SO4 → HCl + NaHSO4 The second step of the process is endothermic, requiring energy input: :NaCl + NaHSO4 → HCl + Na2SO4 Temperatures in the range 600-700 °C are required.
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Exothermic refers to a transformation in which a closed system releases energy (heat) to the surroundings, expressed by :Q < 0\. When the transformation occurs at constant pressure and without exchange of electrical energy, heat Q is equal to the enthalpy change, i.e. :∆H < 0,Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).Principles of Modern Chemistry, Brooks Cole. p. 617.
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In exothermic chemical reactions, the heat that is released by the reaction takes the form of electromagnetic energy or kinetic energy of molecules. The transition of electrons from one quantum energy level to another causes light to be released. This light is equivalent in energy to the stabilization energy of the energy for the chemical reaction, i.e. the bond energy.
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Consistent with this alternative view is the finding that hypercoordinated molecules based on fluorine ligands, for example PF5 do not have hydride counterparts e.g. phosphorane PH5 which is unknown. The ionic model holds up well in thermochemical calculations. It predicts favorable exothermic formation of PF4+F− from phosphorus trifluoride PF3 and fluorine F2 whereas a similar reaction forming PH4+H− is not favorable.
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Such proteins interact with bilayers only electrostatically, for example, ribonuclease and poly-lysine interact with membranes in this mode. However, typical amphitropic proteins have various hydrophobic anchors that penetrate the interfacial region and reach the hydrocarbon interior of the membrane. Such proteins "deform" the lipid bilayer, decreasing the temperature of lipid fluid-gel transition. The binding is usually a strongly exothermic reaction.
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Styrene will polymerise spontaneously to polystyrene, without the need of external initiators. This is known as autopolymerisation, and will take place at ambient temperatures and above. At 100 °C it will polymerise at a rate of ~2% per hour, and more rapidly than this at higher temperatures. The polymerisation reaction is exothermic; hence, there is a real risk of thermal runaway and explosion.
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2 A graphic display of a common type of IMC data is shown in Fig. 2. At the top is a plot of recorded heat flow (μ W=μ J/s) vs. time from a specimen in a sealed ampoule, due to an exothermic rate process which begins, accelerates, reaches a peak heat flow and then subsides. Such data are directly useful (e.g.
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The synthesis and properties of tetramethylurea were comprehensively described. The reaction of dimethylamine with phosgene in the presence of e. g. 50 % sodium hydroxide solution and subsequent extraction with 1,2-dichloroethane yields tetramethylurea in 95% yield. Synthesis of tetramethylurea from phosgene The reactions with dimethylcarbamoyl chloride or phosgene are highly exothermic and the removal of the resulting dimethylamine hydrochloride requires some effort.
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In designing a circulating fluidized bed, with constant temperature distribution for either endothermic or exothermic reactions, in order to determine the appropriate design for cooling or heating of the circulating fluidized bed reactors, a good approximation of heat transfer rates are necessary for better control so that the reactor can change its performance for different operating conditions.World's Largest Circulating Fluidized Bed Boiler Begins Commercial Operation, Giglio, 2009, World's Largest Circulating Fluidized Bed Boiler Begins Commercial Operation, Business and Technology for the Global Generation Industry, Electric Power For highly exothermic reactor, it is recommended to keep the conversion of material low and recycle any possible cooled reactants. It is also recommended to separate the components in order of decreasing percentage of material in feed. This will help in reducing the cost of maintenance for the next separation process.
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When the reaction is exothermic (ΔH is negative and energy is released), heat is included as a product, and when the reaction is endothermic (ΔH is positive and energy is consumed), heat is included as a reactant. Hence, whether increasing or decreasing the temperature would favor the forward or the reverse reaction can be determined by applying the same principle as with concentration changes. Take, for example, the reversible reaction of nitrogen gas with hydrogen gas to form ammonia: :N2(g) + 3 H2(g) ⇌ 2 NH3(g) ΔH = -92 kJ mol−1 Because this reaction is exothermic, it produces heat: :N2(g) + 3 H2(g) ⇌ 2 NH3(g) + heat If the temperature were increased, the heat content of the system would increase, so the system would consume some of that heat by shifting the equilibrium to the left, thereby producing less ammonia.
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The Claisen rearrangement is an exothermic, concerted (bond cleavage and recombination) pericyclic reaction. Woodward–Hoffmann rules show a suprafacial, stereospecific reaction pathway. The kinetics are of the first order and the whole transformation proceeds through a highly ordered cyclic transition state and is intramolecular. Crossover experiments eliminate the possibility of the rearrangement occurring via an intermolecular reaction mechanism and are consistent with an intramolecular process.
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Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. If decomposition is sufficiently exothermic, a positive feedback loop is created producing thermal runaway and possibly an explosion or other chemical reactions.
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Flame inside HCl oven Very pure hydrogen chloride is produced by combining chlorine and hydrogen: :Cl2 \+ H2 → 2 HCl As the reaction is exothermic, the installation is called an HCl oven or HCl burner. The resulting hydrogen chloride gas is absorbed in deionized water, resulting in chemically pure hydrochloric acid. This reaction can give a very pure product, e.g. for use in the food industry.
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Solution-based polymerization is commonly used today for SAP manufacture of co-polymers, particularly those with the toxic acrylamide monomer. This process is efficient and generally has a lower capital cost base. The solution process uses a water-based monomer solution to produce a mass of reactant polymerized gel. The polymerization's own exothermic reaction energy is used to drive much of the process, helping reduce manufacturing cost.
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Metastable and kinetically persistent species or systems are not considered truly stable in chemistry. Therefore, the term chemically stable should not be used by chemists as a synonym of unreactive because it confuses thermodynamic and kinetic concepts. On the other hand, highly chemically unstable species tend to undergo exothermic unimolar decompositions at high rates. Thus, high chemical instability may sometimes parallel unimolar decompositions at high rates.
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Some mixtures containing peroxides and polymerizable monomers may also exhibit SADTs. For example, mixtures of vinyltrimethoxysilane, peroxides and stabilizers are used commercially for cross-linking polyethylene to make PEX pipe. These mixtures are typically liquid solutions that are shipped to where they are used to graft alkoxysilane groups to polyethylene. In such mixtures decomposition of the peroxide can initiate exothermic radical polymerization of the vinyltrimethoxysilane.
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After reactant preparation, synthesis is initiated by point-heating of a small part (usually the top) of the sample. Once started, a wave of exothermic reaction sweeps through the remaining material. SHS has also been conducted with thin films, liquids, gases, powder–liquid systems, gas suspensions, layered systems, gas-gas systems, and others. Reactions have been conducted in a vacuum and under both inert or reactive gases.
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HF-SbF5 is an extremely corrosive and toxic substance that is sensitive to moisture. As with most strong acids, fluoroantimonic acid can react violently with water due to the exothermic hydration. Only hydrogen fluoride can be used as a solvent for the acid, given that an aqueous solution can not be used. Heating fluoroantimonic acid is dangerous as well, as it decomposes into toxic fluorine gas.
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This implies that the reaction is exothermic. The converse is also true; the standard enthalpy of reaction is positive for an endothermic reaction. This calculation has a tacit assumption of ideal solution between reactants and products where the enthalpy of mixing is zero. For example, for the combustion of methane, CH4 \+ 2 O2 → CO2 \+ 2 H2O: :ΔrH⦵ = [ΔfH⦵(CO2) + 2 ΔfH⦵(H2O)] − [ΔfH⦵(CH4) + 2 ΔfH⦵(O2)].
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The catalyst mainly used in the industry today is a copper-zinc- alumina (Cu/ZnO/Al2O3) based catalyst. Also the LTS catalyst has to be activated by reduction before it can be used. The reduction reaction CuO + H2 →Cu + H2O is highly exothermic and should be conducted in dry gas for an optimal result. As for the HTS catalyst mechanism, two similar reaction mechanisms are suggested.
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For example, the hydroxyl is a powerful, non-selective oxidant. Oxidation of an organic compound by Fenton's reagent is rapid and exothermic and results in the oxidation of contaminants to primarily carbon dioxide and water. Reaction () was suggested by Haber and Weiss in the 1930s as part of what would become the Haber–Weiss reaction. Iron(II) sulfate is typically used as the iron catalyst.
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Hydrogen required for this reaction can be produced by aqueous phase catalytic reforming of sorbitol. :19 C6H14O6 → 13 C6H14 \+ 36 CO2 \+ 42 H2O The above chemical reaction is exothermic, and 1.5 moles of sorbitol generate approximately 1 mole of hexane. When hydrogen is co-fed, no carbon dioxide is produced. Sorbitol based polyols are used in the production of polyurethane foam for the construction industry.
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This transition from amorphous solid to crystalline solid is an exothermic process, and results in a peak in the DSC signal. As the temperature increases the sample eventually reaches its melting temperature (Tm). The melting process results in an endothermic peak in the DSC curve. The ability to determine transition temperatures and enthalpies makes DSC a valuable tool in producing phase diagrams for various chemical systems.
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This is different than sodium sulfate which has an exothermic disassociation. The exact energy of disassociation is difficult to quantify as it seems relative to the mols of the salt added. Small amounts of dissolved lithium sulfate have a much greater temperature change than large amounts.Thomson T. P.; Smith D. E.; Wood R. H. Enthalpy of dilution of aqueous Na2SO4 and Si2SO4 J Chem. Eng.
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As ammonium nitrate is a salt, both the cation, NH4+, and the anion, NO3−, may take part in chemical reactions. Solid ammonium nitrate decomposes on heating. At temperatures below around 300 °C, the decomposition mainly produces nitrous oxide and water: : NH4NO3 → N2O + 2H2O At higher temperatures, the following reaction predominates. : 2NH4NO3 → 2N2 \+ O2 \+ 4H2O Both decomposition reactions are exothermic and their products are gas.
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Its mass fraction gravitational binding energy would then be 0.187, −18.7% (exothermic). This is not near 0.6/2 = 0.3, −30%. The equation of state for a neutron star is not yet known. It is assumed that it differs significantly from that of a white dwarf, whose equation of state is that of a degenerate gas that can be described in close agreement with special relativity.
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The ideal mechanism does not absorb any power, which means the power input is equal to the power output. An example is the automobile engine (internal combustion engine) which burns fuel (an exothermic chemical reaction) inside a cylinder and uses the expanding gases to drive a piston."Internal combustion engine", Concise Encyclopedia of Science and Technology, Third Edition, Sybil P. Parker, ed. McGraw-Hill, Inc.
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Because the polymerizing object is no longer in contact with the bottom of the resin vat, mechanical cleavage is not necessary, making CLIP a continuous stereolithographic process. CLIP is being used by Carbon 3D to manufacture parts approximately 100 times faster than traditional SLA methodologies. At these print speeds, however, the heat generated from the exothermic polymerization reactions can result in deformation of the printed object.
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There are many different types of drying oils, including linseed oil, tung oil, and walnut oil. These contain high levels of polyunsaturated fatty acids. Drying oils cure through an exothermic reaction between the polyunsaturated portion of the oil and oxygen from the air. Originally, the term "varnish" referred to finishes that were made entirely of resin dissolved in suitable solvents, either ethanol (alcohol) or turpentine.
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This method utilized a pill containing compounds that dissolved with a strong exothermic reaction without the use of an external heat source. The pill consisted primarily of citric acid monohydrate, sodium hydroxide, and copper sulfate, and a color change (cuprous oxide) was used to identify glucose. Some of Dr. Kamlet’s other inventions dealt with animal feed. One such invention used newsprint for cattle feed.
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Rubidium is the chemical element with the symbol Rb and atomic number 37. Rubidium is a very soft, silvery-white metal in the alkali metal group. Rubidium metal shares similarities to potassium metal and caesium metal in physical appearance, softness and conductivity. Rubidium cannot be stored under atmospheric oxygen, as a highly exothermic reaction will ensue, sometimes even resulting in the metal catching fire.
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The typical composition of commercial HTS catalyst has been reported as 74.2% Fe2O3, 10.0% Cr2O3, 0.2% MgO (remaining percentage attributed to volatile components). The chromium acts to stabilize the iron oxide and prevents sintering. The operation of HTS catalysts occurs within the temperature range of 310 °C to 450 °C. The temperature increases along the length of the reactor due to the exothermic nature of the reaction.
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4, 1974, Inventor: Dimiter I. Tchernev. In these applications, their high heat of adsorption and ability to hydrate and dehydrate while maintaining structural stability is exploited. This hygroscopic property coupled with an inherent exothermic (energy releasing) reaction when transitioning from a dehydrated to a hydrated form make natural zeolites useful in harvesting waste heat and solar heat energy. Zeolite manufactured by an Indian Company namely M/s.
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Calcium chloride was sprayed on this road to prevent weathering, giving it a wet appearance even in dry weather. The second largest application of calcium chloride exploits hygroscopic properties and the tackiness of its hydrates. Calcium chloride is highly hygroscopic and its hydration is an exothermic reaction. A concentrated solution keeps a liquid layer on the surface of dirt roads, which suppresses the formation of dust.
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Large over-topping flows are still a problem, as they can scour the foundations if not accounted for in the design. A disadvantage of gravity dams is that due to their large footprint, they are susceptible to uplift pressures which act as a de- stabilising force. Uplift pressures (buoyancy) can be reduced by internal and foundation drainage systems. During construction, the setting concrete produces an exothermic reaction.
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Oxides The alkaline earth metal oxides are formed from the thermal decomposition of the corresponding carbonates. :CaCO3 → CaO + CO2 (at approx. 9000C) In laboratory, they are obtained from calcium: :Mg(OH)2 → MgO + H2O or nitrates: :Ca(NO3)2 → CaO + 2NO2 \+ 1/2O2 The oxides exhibit basic character: they turn phenolphthalein red and litmus, blue. They react with water to form hydroxides in an exothermic reaction.
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These coated granules are usually under the commercial labels Aerojet S-405 (previously made by Shell) or W.C.Heraeus H-KC 12 GA (previously made by Kali Chemie). There is no igniter with hydrazine. Aerojet S-405 is a spontaneous catalyst, that is, hydrazine decomposes on contact with the catalyst. The decomposition is highly exothermic and produces a gas that is a mixture of nitrogen, hydrogen and ammonia.
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In general, the reaction is exothermic, but, e.g., the formation of mercuric oxide (HgO) is endothermic. The charge of the resulting ions is a major factor in the strength of ionic bonding, e.g. a salt C+A− is held together by electrostatic forces roughly four times weaker than C2+A2− according to Coulombs law, where C and A represent a generic cation and anion respectively.
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To keep the catalyst functioning, the respirator has pre-filters of a dust filter and a moisture trap, as either contaminant would reduce its effectiveness. For storage, the respirator must be kept sealed within its case to avoid the catalyst activating and becoming consumed. The catalyst reaction is exothermic and so the respirator and its gas gets hot in use. The case is metal, to conduct some of this heat away.
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These reactions are exothermic and can be used to produce the diborides by SHS. Production of ZrB2 from ZrO2 via SHS often leads to incomplete conversion of reactants, and therefore double SHS (DSHS) has been employed by some researchers. A second SHS reaction with Mg and H3BO3 as reactants along with the ZrB2/ZrO2 mixture yields increased conversion to the diboride, and particle sizes of 25–40 nm at 800 °C.
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Fenton's reagent in particular is highly exothermic and can cause unwanted effects on microbial life in the aquifer if it is not used carefully or stabilized. Further challenges associated with ISCO include the generation of unwanted or toxic oxidation products. Recent evidence suggests that the oxidation of benzene results in the formation of phenol (a relatively benign compound) and a novel aldehyde side-product, the toxicology of which is unknown.
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Adolph Frank The Frank–Caro process, also called cyanamide process, is the nitrogen fixation reaction of calcium carbide with nitrogen gas in a reactor vessel at about 1,000°C. The reaction is exothermic and self-sustaining once the reaction temperature is reached. Originally the reaction took place in large steel cylinders with an electrical resistance element providing initial heat to start the reaction. Modern production uses rotating ovens.
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Proceeding of The 39th IPA Conference and Exhibition, Jakarta, Indonesia, May 2015. The chemical reactions in both cases are exothermic. Large quantities of mix will generate their own heat and greatly speed the reaction, so it is usual to mix small amounts which can be used quickly. While it is common to associate polyester resins and epoxy resins, their properties are sufficiently different that they are properly treated as distinct materials.
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Typical examples of exothermic reactions are precipitation and crystallization, in which ordered solids are formed from disordered gaseous or liquid phases. In contrast, in endothermic reactions, heat is consumed from the environment. This can occur by increasing the entropy of the system, often through the formation of gaseous reaction products, which have high entropy. Since the entropy increases with temperature, many endothermic reactions preferably take place at high temperatures.
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A core shroud is a stainless steel cylinder surrounding a nuclear reactor core whose main function is to direct the cooling water flow. The nuclear reactor core is where the nuclear reactions take place. Because the reactions are exothermic, cool water is needed to prevent the reactor core from melting down. The core shroud helps by directing this cool water towards the reactor core, providing stability to the nuclear reactions.
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Transition metal carbohydrides can be produced by heating a metal carbide in hydrogen, for example at 2000°C and 3 bars. This reaction is exothermic, and just needs to be ignited at a much lower temperature. The process is called self-propagating high-temperature synthesis or SHS. A hydrocarbide may be formed when the metal is milled in a hydrocarbon, for example in the manufacture of titanium carbide.
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This reaction is very exothermic. The change of enthalpy of this reaction is equal to -481.06 kJ. The heat provided by the main reaction serves as a catalyst for other side reactions. :CH4 \+ H2O → CO + 3 H2 :2 CH4 \+ 3 O2 → 2 CO + 4 H2O :4 NH3 \+ 3 O2 → 2 N2 \+ 6 H2O These side reactions can be reduced by only short exposures to the catalyst of the order of 0.0003s.
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Pure 1-Trifluoromethyl-1,2-benziodoxol-3(1H)-one is metastable at room temperature. Heating it above the melting point will lead to strong exothermic decomposition, in which trifluoroiodomethane (CF3I) is released. The heat of composition at a temperature of 149 °C and higher has been determined to be 502 J·g−1.From recrystallization in acetonitrile, small amounts of trifluoromethyl-2-iodobenzoate and 2-iodobenzyl fluoride were observed as decomposition products.
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The cover was drawn by Paul Whitehead, and was inspired by "Pioneers Over c". The front cover was a painting he had already completed, called "Birthday", which showed a beam of light focusing on London, illustrating Whitehead's birth. The inner gatefold picture was called "Checkmate". "H to He" in the title refers to the fusion of hydrogen nuclei to form helium nuclei, a basic exothermic reaction between the sun and stars.
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The reaction is irreversible and exothermic, releasing 1.26–1.6 kJ/mol. An additional factor in determining the structure of water ice is deposition rate. Even if it is cold enough to form amorphous ice, crystalline ice will form if the flux of water vapor onto the substrate is less than a temperature-dependent critical flux. This effect is important to consider in astrophysical environments where the water flux can be low.
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The filler gives the composite greater strength, wear resistance, decreased polymerisation shrinkage, improved translucency, fluorescence and colour, and a reduced exothermic reaction on polymerisation. It also however causes the resin composite to become more brittle with an increased elastic modulus. Glass fillers are found in multiple different compositions allowing an improvement on the optical and mechanical properties of the material. Ceramic fillers include zirconia-silica and zirconium oxide.
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If the anisotropy is large enough, the dendrite may present a faceted morphology. The microstructural length scale is determined by the interplay or balance between the surface energy and the temperature gradient (which drives the heat/solute diffusion) in the liquid at the interface.J. A. Dantzig, M. Rappaz,Solidification, EPFL Press, 2009, pp. 287–298, As solidification proceeds, an increasing number of atoms lose their kinetic energy, making the process exothermic.
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The Ugi reaction is a multi-component reaction in organic chemistry involving a ketone or aldehyde, an amine, an isocyanide and a carboxylic acid to form a bis-amide. The reaction is named after Ivar Karl Ugi, who first reported this reaction in 1959. The Ugi reaction The Ugi reaction is exothermic and usually complete within minutes of adding the isocyanide. High concentration (0.5M - 2.0M) of reactants give the highest yields.
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The reaction is exothermic with ΔH -41.1 kJ/mol and have an adiabatic temperature rise of 8–10 °C per percent CO converted to CO2 and H2. The most common catalysts used in the water-gas shift reaction are the high temperature shift (HTS) catalyst and the low temperature shift (LTS) catalyst. The HTS catalyst consists of iron oxide stabilized by chromium oxide, while the LTS catalyst is based on copper.
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Closely analogous considerations apply in chemical and nuclear reactions. Exothermic chemical reactions in closed systems do not change mass, but do become less massive once the heat of reaction is removed, though this mass change is too small to measure with standard equipment. In nuclear reactions, the fraction of mass that may be removed as light or heat, i.e. binding energy, is often a much larger fraction of the system mass.
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Gaseous solutes exhibit more complex behavior with temperature. As the temperature is raised, gases usually become less soluble in water (exothermic dissolution reaction related to their hydration) (to minimum, which is below 120 °C for most permanent gases), but more soluble in organic solvents (endothermic dissolution reaction related to their solvatation). The chart shows solubility curves for some typical solid inorganic salts (temperature is in degrees Celsius i.e. kelvins minus 273.15).
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If this is not done properly, the charcoal that has been produced burns within a very short time under great heat (exothermic reaction). The heat generated in this process is so great that it is impossible to approach the pile. The coal must now cool down for at least 12 hours. If the charcoal is too small it remains in the pile and is mixed with the ash.
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Upon dissolution in water, which is highly exothermic, the hydrogen halides give the corresponding acids. These acids are very strong, reflecting their tendency to ionize in aqueous solution yielding hydronium ions (H3O+). With the exception of hydrofluoric acid, the hydrogen halides are strong acids, with acid strength increasing down the group. Hydrofluoric acid is complicated because its strength depends on the concentration owing to the effects of homoconjugation.
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In the canonical ensemble, amount of substance (N), volume (V) and temperature (T) are conserved. It is also sometimes called constant temperature molecular dynamics (CTMD). In NVT, the energy of endothermic and exothermic processes is exchanged with a thermostat. A variety of thermostat algorithms are available to add and remove energy from the boundaries of an MD simulation in a more or less realistic way, approximating the canonical ensemble.
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A fusion process that produces nuclei lighter than iron-56 or nickel-62 will generally release energy. These elements have relatively small mass per nucleon and large binding energy per nucleon. Fusion of nuclei lighter than these releases energy (an exothermic process), while fusion of heavier nuclei results in energy retained by the product nucleons, and the resulting reaction is endothermic. The opposite is true for the reverse process, nuclear fission.
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Trifluoroacetic acid is a corrosive acid but it does not pose the hazards associated with hydrofluoric acid because the carbon-fluorine bond is not labile. Only if heated or treated with ultrasonic waves will it decompose into hydrofluoric acid. TFA is harmful when inhaled, causes severe skin burns and is toxic for aquatic organisms even at low concentrations. TFA's reaction with bases and metals, especially light metals, is strongly exothermic.
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A thermite mixture using iron (III) oxide Thermite () entry "thermite" is a pyrotechnic composition of metal powder and metal oxide. When ignited by heat, thermite undergoes an exothermic reduction-oxidation (redox) reaction. Most varieties are not explosive, but can create brief bursts of heat and high temperature in a small area. Its form of action is similar to that of other fuel-oxidizer mixtures, such as black powder.
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Organic peroxides are useful in chemical synthesis due to their propensity to decompose. In doing so they generate useful radicals that can initiate polymerization to create polymers, modify polymers by grafting or visbreaking, or cross-link polymers to create a thermoset. When used for these purposes, the peroxide is highly diluted, so the heat generated by the exothermic decomposition is safely absorbed by the surrounding medium (e.g. polymer compound or emulsion).
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Since the polymerization reactions involved in SLA are highly exothermic processes, the production of objects at high-throughputs is associated with high temperatures that can result in structural defects. HARP addresses this problem by utilizing a solid-liquid slip boundary (Figure 2) that cools the resin by withdrawing heat from the system. This allows for large structures to be fabricated quickly without the temperature-associated defects inherent to other SLA processes.
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Reactive bonding describes a wafer bonding procedure using highly reactive nanoscale multilayer systems as an intermediate layer between the bonding substrates. The multilayer system consists of two alternating different thin metallic films. The self-propagating exothermic reaction within the multilayer system contributes the local heat to bond the solder films. Based on the limited temperature the substrate material is exposed, temperature-sensitive components and materials with different CTEs, i.e.
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Image of multilayer system as reactive layer on a silicon wafer by Fraunhofer ENAS The bonding is based on reactive nano scale multilayers providing an internal heat source. These foils are combined with additional solder layers to achieve bonding. The heat that is required for the bonding is created by a self- propagating exothermic reaction of the multilayer system. This reaction is ignited by an energy pulse, i.e.
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Beyond Tg, molten glass becomes prone to devitrification. This transformation is commonly evidenced by differential thermal analysis (DTA). Two characteristic temperatures are measured from the DTA curve: Tx corresponds to the onset of crystallization and Tc is taken at the maximum of the exothermic peak. Glass scientists also use liquidus temperature TL. Beyond this temperature liquid does not produce any crystal and it may remain indefinitely in the liquid state.
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Ss. Cyril and Methodius University, Skopje, Macedonia. Ammonium dichromate decomposition The volcano demonstration involves igniting a pile of the salt, which initiates the following exothermic conversion:- :(s) → (s) + (g) + 4(g) (ΔH = −429.1±3 kcal/mol) Like ammonium nitrate, it is thermodynamically unstable. Its decomposition reaction proceeds to completion once initiated, producing voluminous dark green powdered chromium(III) oxide. Not all of the ammonium dichromate decomposes in this reaction.
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Diborane has been tested as a rocket propellant. Complete combustion is strongly exothermic. However, combustion is not complete in the rocket engine, as some boron monoxide, B2O, is produced. This mirrors the incomplete combustion of hydrocarbons, to produce carbon monoxide, CO. Diborane has been used as a rubber vulcaniser, as a catalyst for hydrocarbon polymerisation, as a flame-speed accelerator, and as a doping agent for the production of semiconductors.
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Urea plant using ammonium carbamate briquettes, Fixed Nitrogen Research Laboratory, ca. 1930 The basic process, developed in 1922, is also called the Bosch–Meiser urea process after its discoverers. Various commercial urea processes are characterized by the conditions under which urea forms and the way that unconverted reactants are further processed. The process consists of two main equilibrium reactions, with incomplete conversion of the reactants. The first is carbamate formation: the fast exothermic reaction of liquid ammonia with gaseous carbon dioxide (CO2) at high temperature and pressure to form ammonium carbamate (H2N-COONH4): :2 NH3 \+ CO2 H2N-COONH4 (ΔH= -117kJ/mol at 110 atm and 160°C) The second is urea conversion: the slower endothermic decomposition of ammonium carbamate into urea and water: :H2N-COONH4 (NH2)2CO + H2O (ΔH= +15.5 kJ/mol at 160-180°C) The overall conversion of NH3 and CO2 to urea is exothermic, the reaction heat from the first reaction driving the second.
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Chlorination favors the products because it is an exothermic reaction, which means that the products are lower in energy than the reactants. When looking at the adjacent diagram (representation of an "early" transition state), one must focus on the transition state, which is not able to be observed during an experiment. To understand what is meant by an “early” transition state, the Hammond postulate represents a curve that shows the kinetics of this reaction.
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Particularly exothermic fermentations may require the use of external heat exchangers. Nutrients may be continuously added to the fermenter, as in a fed-batch system, or may be charged into the reactor at the beginning of fermentation. The pH of the medium is measured and adjusted with small amounts of acid or base, depending upon the fermentation. For aerobic (and some anaerobic) fermentations, reactant gases (especially oxygen) must be added to the fermentation.
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Due to its chemical composition, a Cetane Improver additive has the faculty to decompose itself at lower temperature than Diesel fuel. The additive’s exothermic decomposition leads to successive fuel reactions that result in the start of the combustion at low temperature. Effects of Cetane Improver on Ignition Delay The effect of the additive varies with the fuel type, which itself depends on the quality of the crude oil and the way it is refined.
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Synthesis of involves direct reaction of molybdenum and selenium in a sealed tube at high temperature. Chemical vapor transport with a halogen (usually bromine or iodine) is used to purify the compound at very low pressure (less than 10-6 torr) and very high temperature (600–700 °C). It has to be heated very gradually to prevent explosion due to its strong exothermic reaction. Stoichiometric layers crystallize in a hexagonal structure as the sample cools.
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Chemical reactions are determined by the laws of thermodynamics. Reactions can proceed by themselves if they are exergonic, that is if they release energy. The associated free energy of the reaction is composed of two different thermodynamic quantities, enthalpy and entropy:Atkins, pp. 106–108 :; \Delta G = \Delta H - T \cdot \Delta S. :: : free energy, : enthalpy, : temperature, : entropy, : difference(change between original and product) Reactions can be exothermic, where ΔH is negative and energy is released.
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Chlorination favors the products because it is an exothermic reaction, which means that the products are lower in energy than the reactants. When looking at the adjacent diagram (representation of an "early" transition state), one must focus on the transition state, which is not able to be observed during an experiment. To understand what is meant by an “early” transition state, the Hammond postulate represents a curve that shows the kinetics of this reaction.
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Gasoline can In fire protection, an accelerant is any substance or mixture that accelerates or speeds the development and escalation of fire. Accelerants are often used to commit arson, and some accelerants may cause an explosion. Some fire investigators use the term "accelerant" to mean any substance that initiates and promotes a fire without implying intent or malice. A fire is a self-sustaining, exothermic oxidation reaction that emits heat and light.
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For the alkali metals, amalgamation is exothermic, and distinct chemical forms can be identified, such as KHg and KHg2. KHg is a gold-coloured compound with a melting point of 178 °C, and KHg2 a silver-coloured compound with a melting point of 278 °C. These amalgams are very sensitive to air and water, but can be worked with under dry nitrogen. The Hg-Hg distance is around 300 picometres, Hg-K around 358 pm.
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The reaction is highly exothermic and rock temperatures can be raised by about , providing an energy source for formation of non-volcanic hydrothermal vents. The magnetite-forming chemical reactions produce hydrogen gas under anaerobic conditions prevailing deep in the mantle, far from the Earth's atmosphere. Carbonates and sulfates are subsequently reduced by hydrogen and form methane and hydrogen sulfide. The hydrogen, methane, and hydrogen sulfide provide energy sources for deep sea chemotroph microorganisms.
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Gasification :CH4 \+ H2O → CO + 3 H2 In a second stage, additional hydrogen is generated through the lower-temperature, exothermic, water gas shift reaction, performed at about 360 °C: :CO + H2O → CO2 \+ H2 Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.
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A fire requires heat, fuel, and an oxidizing agent. The energy required to overcome the activation energy barrier for combustion is transferred as heat into the system, resulting in changes to the system’s internal energy. In a process, the energy input to start a fire may comprise both work and heat, such as when one rubs tinder (work) and experiences friction (heat) to start a fire. The ensuing combustion is highly exothermic, which releases heat.
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Partial oxidation is a third way for producing hydrogen from methanol. The reaction is given below, and is often carried out with air or oxygen as oxidant : The reaction is exothermic and has, under favorable conditions, a higher reaction rate than steam reforming. The catalyst used is often Cu (Cu/ZnO) or Pd and they differ in qualities such as by-product formation, product distribution and the effect of oxygen partial pressure.
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They are sufficiently brittle and rigid enough to maintain open fractures. Some of the gas produced is held in natural fractures, some in pore spaces, and some is adsorbed onto the shale matrix. Further, the adsorption of gas is a process of physisorption, exothermic and spontaneous. The gas in the fractures is produced immediately; the gas adsorbed onto organic material is released as the formation pressure is drawn down by the well.
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However, if the energy dissipated at the failure point is high enough, a self-sustaining exothermic reaction can start, similar to the thermite reaction, with metallic tantalum as fuel and manganese dioxide as oxidizer. This undesirable reaction will destroy the capacitor, producing smoke and possibly flame. Therefore, tantalum capacitors can be freely deployed in small-signal circuits, but application in high-power circuits must be carefully designed to avoid thermal runaway failures.
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VCM and water are introduced into the reactor along with a polymerization initiator and other additives. The contents of the reaction vessel are pressurized and continually mixed to maintain the suspension and ensure a uniform particle size of the PVC resin. The reaction is exothermic and thus requires cooling. As the volume is reduced during the reaction (PVC is denser than VCM), water is continually added to the mixture to maintain the suspension.
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Abiotic sources of hydrogen gas include water-rock and photochemical reactions. Exothermic serpentinization reactions between water and olivine minerals produce H2 in the marine or terrestrial subsurface. In the ocean, hydrothermal vents erupt magma and altered seawater fluids including abundant H2, depending on the temperature regime and host rock composition. Molecular hydrogen can also be produced through photooxidation (via solar UV radiation) of some mineral species such as siderite in anoxic aqueous environments.
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Some insect larvae feed on the detritus.D.A. Grimaldi, 2005 Fungi and bacteria continue the decomposition processB.C. Patten, 1975 after grazers have consumed larger elements of the organic materials, and animal trampling has assisted in mechanically breaking down organic matter. At the later stages of decomposition, mesophilic micro-organisms decompose residual detritus, generating heat from exothermic processes; such heat generation is associated with the well known phenomenon of the elevated temperature of composting.
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Acetylene reacts with anhydrous hydrogen chloride gas over a mercuric chloride catalyst to give vinyl chloride: :C2H2 \+ HCl → CH2=CHCl The reaction is exothermic and highly selective. Product purity and yields are generally very high. This industrial route to vinyl chloride was common before ethylene became widely distributed. When vinyl chloride producers shifted to using the thermal cracking of EDC described above, some used byproduct HCl in conjunction with a colocated acetylene-based unit.
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The sign convention is the same as for enthalpy of reaction: when the enthalpy of mixing is positive, mixing is endothermic while negative enthalpy of mixing signifies exothermic mixing. In ideal mixtures the enthalpy of mixing is null. In non-ideal mixtures the thermodynamic activity of each component is different from its concentration by multiplying with the activity coefficient. One approximation for calculating the heat of mixing is Flory–Huggins solution theory for polymer solutions.
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A concentrated solution of hydrogen peroxide is known as high test peroxide and decomposes to produce oxygen and water (steam). : 2 H2O2 → 2 H2O + O2 Hydrazine decomposes to nitrogen and hydrogen. The reaction is strongly exothermic and produces high volume of hot gas from small volume of liquid. #3 N2H4 → 4 NH3 \+ N2 #N2H4 → N2 \+ 2 H2 #4 NH3 \+ N2H4 → 3 N2 \+ 8 H2 Many solid rocket propellant compositions can be used as gas generators.
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In ethanol fermentation, (1) one glucose molecule breaks down into two pyruvates. The energy from this exothermic reaction is not used to bind the inorganic phosphates to ADP and convert NAD+ to NADH. (2) The two pyruvates are then broken down into two acetaldehydes and give off two CO2 as a by- product. (3) The two acetaldehydes are then converted to two ethanol by using the H- ions from NADH, converting NAD back into NADH.
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Pressurized commercial airplanes have an emergency supply of automatically supplied to the passengers in case of cabin depressurization. Sudden cabin pressure loss activates chemical oxygen generators above each seat, causing oxygen masks to drop. Pulling on the masks "to start the flow of oxygen" as cabin safety instructions dictate, forces iron filings into the sodium chlorate inside the canister. A steady stream of oxygen gas is then produced by the exothermic reaction.
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These are highly flammable in their liquid state. All drying oils, certain alkyds (including paints), and many polyurethanes produce heat (an exothermic reaction) during the curing process. Thus, oil-soaked rags and paper can smolder and ignite into flames, even several hours after use if proper precautions are not taken. Therefore, many manufacturers list proper disposal practices for rags and other items used to apply the finish, such as disposal in a water filled container.
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APS and PAPS are intermediates in the reduction of sulfate to sulfite, an exothermic conversion that is carried out by sulfate-reducing bacteria. In these organisms, sulfate serves as an electron acceptor, akin to the use of O2 as an electron acceptor by aerobic organisms. Sulfate is not reduced directly but must be activated by the formation of APS or PAPS. These carriers of activated sulfate are produced by reaction with ATP.
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Methyl, ethyl, and other alkyl or aralkyl halides that are not dehydrohalogenated readily can react with aluminium metal in an exothermic process to form organoaluminium sesquihalides in high yields. An important example is the reaction of ethyl chloride with aluminium to form ethylaluminium sesquichloride. :3 C2H5Cl + 2 Al → (C2H5)3Al2Cl3 The reaction is carried out with aluminium in the form of turnings, shavings, granules, or powder. Oxygen and moisture must be rigorously excluded.
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A bridgewire, sometimes spelled as bridge wire, also known as a hot bridge wire (HBW) is a relatively thin resistance wire used to set off a pyrotechnic composition serving as pyrotechnic initiator. By passing of electric current it is heated to a high temperature that starts the exothermic chemical reaction of the attached composition. After successful firing, the bridgewire melts, resulting in an open circuit. Usually a thin nichrome wire is used.
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These worked well but had the disadvantage of having to be stored in the refrigerator, were exothermic so they stung the patient, and the bond was brittle. Nowadays, the longer chain polymer, 2-octyl cyanoacrylate, is the preferred medical grade glue. It is available under various trade names, such as LiquiBand, SurgiSeal, FloraSeal, and Dermabond. These have the advantages of being more flexible, making a stronger bond, and being easier to use.
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Mechanism for the formation of the epoxide product This reaction is exothermic due to the stability of nitrogen gas and the carbonyl containing compounds. This specific mechanism is supported by several observations. First, kinetic studies of reactions between diazomethane and various ketones have shown that the overall reaction follows second order kinetics. Additionally, the reactivity of two series of ketones are in the orders Cl3CCOCH3 > CH3COCH3 > C6H5COCH3 and cyclohexanone > cyclopentanone > cycloheptanone > cyclooctanone.
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Reactions involving diazomethanes with alkyl or aryl substituents are exothermic at or below room temperature. Reactions involving diazomethanes with acyl or aroyl substituents require higher temperatures. The reaction has since been modified to proceed in the presence of Lewis acids and common organic solvents such as THF and dichloromethane. Reactions generally run at room temperature for about an hour, and the yield ranges from 70%-80% based on the choice of Lewis acid and solvent.
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It produces thermostable hemicellulases that degrade hemicellulose of plant biomass into simpler sugars. As the temperature in compost systems rises, the pioneer flora disappears and thermophilic fungi become dominant. Exothermic reactions of saprophytic and mesophilc microflora raise the temperature to 40 °C, which causes thermophilic spores to germinate and eventually outgrow pioneers, raising the temperature even higher to 60 °C. Around the end of decomposition, thermophilic fungi compose 50-70% of compost biomass.
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Sodium methoxide is prepared by treating methanol with sodium: :2 Na + 2 → 2 + The reaction is so exothermic that ignition is possible. The resulting solution, which is colorless, is often used as a source of sodium methoxide, but the pure material can be isolated by evaporation followed by heating to remove residual methanol. The solid hydrolyzes in water to give methanol and sodium hydroxide. Indeed, samples of sodium methoxide are often contaminated with sodium hydroxide.
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The oxygen oxidizes the hydroquinones and also acts as the propellant. The oxidation reaction is very exothermic (ΔH = −202.8 kJ/mol) and rapidly heats the mixture to the boiling point. Long-lived queens of the termite Reticulitermes speratus have significantly lower oxidative damage to their DNA than non-reproductive individuals (workers and soldiers). Queens have more than two times higher catalase activity and seven times higher expression levels of the catalase gene RsCAT1 than workers.
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The proton affinity (PA, Epa) of an anion or of a neutral atom or molecule is the negative of the enthalpy change in the reaction between above species and proton in the gas phase:"Proton affinity." Compendium of Chemical Terminology. ::: A- + H+ -> HA ::: B + H+ -> BH+ These reactions are always exothermic in the gas phase, i.e. energy is released when the reaction advances in the direction shown and enthalpy is negative, while the proton affinity is positive.
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An exothermic weld has higher mechanical strength than other forms of weld, and excellent corrosion resistance It is also highly stable when subject to repeated short-circuit pulses, and does not suffer from increased electrical resistance over the lifetime of the installation. However, the process is costly relative to other welding processes, requires a supply of replaceable moulds, suffers from a lack of repeatability, and can be impeded by wet conditions or bad weather (when performed outdoors).
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Self- heating field rations for up to 18 soldiers For critical vaccines, insulated shipping containers are passive packaging to help control the temperatures fluctuations seen even with a controlled cold chain. In addition, gel packs are often used to keep the temperature of the contents within specified acceptable temperature ranges. Some newer packages have the ability to heat or cool the product for the consumer. These have segregated compartments where exothermic or endothermic reactions provide the desired effect.
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They are also thought to influence the dynamics of mantle convection in that the exothermic transitions reinforce flow across the phase boundary, whereas the endothermic reaction hampers it. The pressure at which these phase transitions occur depends on temperature and iron content. At , the pure magnesium end member, forsterite, transforms to wadsleyite at and to ringwoodite at pressures above . Increasing the iron content decreases the pressure of the phase transition and narrows the wadsleyite stability field.
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For example, in an exothermic reaction the transition state is closer in energy to the reactants than to the products. Therefore, the transition state will be more geometrically similar to the reactants than to the products. In contrast, however, in an endothermic reaction the transition state is closer in energy to the products than to the reactants. So, according to Hammond’s postulate the structure of the transition state would resemble the products more than the reactants.
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Aluminothermy started from the experiments of Russian scientist Nikolay Beketov at the University of Kharkiv in Ukraine, who proved that aluminium restored metals from their oxides under high temperatures. The reaction was first used for the carbon-free reduction of metal oxides. The reaction is highly exothermic, but it has a high activation energy since strong interatomic bonds in the solids must be broken first. The oxide was heated with aluminium in a crucible in a furnace.
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The energy from fission is used to generate electric power in hundreds of locations worldwide. Nuclear energy is also released during atomic fusion, when light nuclei like hydrogen are combined to form heavier nuclei such as helium. The Sun and other stars use nuclear fusion to generate thermal energy which is later radiated from the surface, a type of stellar nucleosynthesis. In any exothermic nuclear process, nuclear mass might ultimately be converted to thermal energy, given off as heat.
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Steam power to fire the piston was generated by the violent exothermic chemical reaction created when hydrogen peroxide and potassium permanganate (termed T-Stoff and Z-Stoff) are combined. The principal military use of the pulsejet engine, with the volume production of the Argus As 014 unit (the first pulsejet engine ever in volume production), was for use with the V-1 flying bomb. The engine's characteristic droning noise earned it the nicknames "buzz bomb" or "doodlebug".
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Generic potential energy diagram showing the effect of a catalyst in a hypothetical exothermic chemical reaction X + Y to give Z. The presence of the catalyst opens a different reaction pathway (shown in red) with a lower activation energy. The final result and the overall thermodynamics are the same. Catalysts work by providing an (alternative) mechanism involving a different transition state and lower activation energy. Consequently, more molecular collisions have the energy needed to reach the transition state.
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As lithium migrates out of the cathode in a cell, the undergoes non-linear expansion that affects the structural integrity of the cell. The fully lithiated and unlithiated states of are structurally similar which means that cells are more structurally stable than cells. No lithium remains in the cathode of a fully charged cell. (In a cell, approximately 50% remains.) is highly resilient during oxygen loss, which typically results in an exothermic reaction in other lithium cells.
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For example, in an exothermic reaction the transition state is closer in energy to the reactants than to the products. Therefore, the transition state will be more geometrically similar to the reactants than to the products. In contrast, however, in an endothermic reaction the transition state is closer in energy to the products than to the reactants. So, according to Hammond's postulate the structure of the transition state would resemble the products more than the reactants.
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Monopropellants are propellants consisting of chemicals that release energy through exothermic chemical decomposition. The molecular bond energy of the monopropellant is released usually through use of a catalyst. This can be contrasted with bipropellants that release energy through the chemical reaction between an oxidizer and a fuel. While stable under defined storage conditions, monopropellants decompose very rapidly under certain other conditions to produce a large volume of energetic (hot) gases for the performance of mechanical work.
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Issues with thermal stability are better for cathodes than other nickel-rich chemistries although not significantly. This makes batteries susceptible to thermal runaway in cases of abuse such as high temperature operation (>130 °C) or overcharging. At elevated temperatures, decomposition generates oxygen, which then reacts with the organic electrolyte of the cell. This is a safety concern due to the magnitude of this highly exothermic reaction, which can spread to adjacent cells or ignite nearby combustible material.
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Dental composite resin. As with other composite materials, a dental composite typically consists of a resin-based oligomer matrix, such as a bisphenol A-glycidyl methacrylate (BISGMA), urethane dimethacrylate (UDMA) or semi-crystalline polyceram (PEX), and an inorganic filler such as silicon dioxide (silica). Without a filler the resin wears easily, exhibits high shrinkage and is exothermic. Compositions vary widely, with proprietary mixes of resins forming the matrix, as well as engineered filler glasses and glass ceramics.
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In its usual format, SHS is conducted starting from finely powdered reactants that are intimately mixed. In some cases, the reagents are finely powdered whereas in other cases, they are sintered to minimize their surface area and prevent uninitiated exothermic reactions, which can be dangerous. In other cases, the particles are mechanically activated through techniques such as high energy ball milling (e.g. in a planetary mill), which results in nanocomposite particles that contain both reactants within individual chemical cells.
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Blue Organic Electrophosphorescence Using Exothermic Host–Guest Energy Transfer. Russell J. Holmes, S.R. Forrest, Yeh J. Tung, Raymond C. Kwong, Julie J. Brown, Simona Garon, Mark E. Thompson, Applied Physics Letters, 2003, 82(15), 2422-2424.Blue and Near-UV Phosphorescence from Iridium Complexes with Cyclometalated Pyrazolyl or N-Heterocyclic Carbene Ligands. T. Sajoto, P. Djurovich, A. Tamayo, M. Yousufuddin, R. Bau, M. E. Thompson, R. J. Holmes, and S.R. Forrest, Inorganic Chemistry, 2005, 44(22), 7992-8003.
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Personal protective equipment should always be used when using bleach. Bleach should never be mixed with vinegar or other acids as this will create highly toxic chlorine gas and can cause severe burns internally and externally. Mixing bleach with ammonia similarly produces toxic chloramine gas, which can burn the lungs. Mixing bleach with hydrogen peroxide results in an exothermic chemical reaction that releases oxygen, and may cause the contents to splatter and cause skin and eye injury.
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Air-activated hand warmers contain cellulose, iron, activated carbon, vermiculite (which holds water) and salt and produce heat from the exothermic oxidation of iron when exposed to air. They typically emit heat for 1 to 10 hours, it usually takes 15-30 minutes to start to heat up, although the heat given off rapidly diminishes after 1–2 hours. The oxygen molecules in the air react with iron, forming rust. Salt is often added to catalyze the process.
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A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride. When scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms; when rubbed with a pestle in a mortar, a strong detonation occurs. Black antimony is formed upon rapid cooling of antimony vapor. It has the same crystal structure as red phosphorus and black arsenic; it oxidizes in air and may ignite spontaneously.
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MgO2 can be produced by mixing MgO with hydrogen peroxide to create magnesium peroxide and water. This being an exothermic reaction should be cooled and kept around 30–40 degrees Celsius. It is also important to remove as much iron from the reaction environment as possible due to iron's ability to catalyze the degradation of the peroxide. The addition of oxygen stabilizers such as sodium silicate can also be used to help prevent the premature degradation of the peroxide.
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Lithium sulfate is soluble in water, though it does not follow the usual trend of solubility versus temperature — its solubility in water decreases with increasing temperature, as its dissolution is an exothermic process. This property is shared with few inorganic compounds, such as the lanthanoid sulfates. Lithium sulfate crystals, being piezoelectric, are also used in ultrasound-type non-destructive testing because they are very efficient sound receivers. However, they do suffer in this application because of their water solubility.
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As the hemiacetonitrile solvatated isolated compound expels solvent at 100 °C, and shows then in the DSC measurement from 240 °C onwards a strong exothermic reaction with a generated heat of 2300 J·g−1. The enthalpies are higher than that of sodium azide with −800 J·g−1,T. Grewer: Thermal Hazards of Chemical Reactions, Industrial Safety Series 4, Elsevier 1994. but still lower than the values encountered with classic explosives such as RDX with −4500 J·g−1.
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In the real world, the 100 eV from the deposited atom would rapidly be transported through and shared among a large number of atoms (10^{10} or more) with no big change in temperature. When there are only 500 atoms, however, the substrate is almost immediately vaporized by the deposition. Something similar happens in biophysical simulations. The temperature of the system in NVE is naturally raised when macromolecules such as proteins undergo exothermic conformational changes and binding.
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Standard state does not strictly specify a temperature, but expressions for enthalpy generally reference the standard heat of formation at . For endothermic processes, the change is a positive value, and is negative in exothermic (heat-releasing) processes. The enthalpy of an ideal gas is independent of its pressure, and depends only on its temperature, which correlates to its internal energy. Real gases at common temperatures and pressures often closely approximate this behavior, which simplifies practical thermodynamic design and analysis.
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57, p.50. Online version :Et2NSiMe3 \+ SF4 → Et2NSF3 \+ Me3SiF The original paper calls for trichlorofluoromethane (Freon-11) as a solvent, a compound that has been banned under the Montreal Protocol and is no longer available as a commodity chemical. diethyl ether is a green alternative that can be used with no decrease in yield. Because of the dangers involved in the preparation of DAST (glass etching, possibility of exothermic events), it is often purchased from a commercial source.
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One method of preparing GaBr3 is to heat elemental gallium in the presence of bromine liquid under vacuum. Following the highly exothermic reaction, the mixture is allowed to rest and then subjected to various purifying steps. This method from the turn of the twentieth century remains a useful way of preparing GaBr3. Historically Gallium was obtained by electrolysis of its hydroxide in KOH solution, however today it is obtained as a byproduct of Aluminum and Zinc production.
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In the commercial process for producing non-stoichiometric TiH(2-x), titanium metal sponge is treated with hydrogen gas at atmospheric pressure at between 300-500 °C. Absorption of hydrogen is exothermic and rapid, changing the color of the sponge grey/black. The brittle product is ground to a powder, which has a composition around TiH1.95. In the laboratory, titanium hydride is produced by heating titanium powder under flowing hydrogen at 700 °C, the idealized equation being:M.
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IMC accomplishes this dynamic analysis by measuring and recording vs. elapsed time the net rate of heat flow (μJ/sec = μW) to or from the specimen ampoule, and the cumulative amount of heat (J) consumed or produced. IMC is a powerful and versatile analytical tool for four closely related reasons: # All chemical and physical processes are either exothermic or endothermic—produce or consume heat. # The rate of heat flow is proportional to the rate of the process taking place.
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Bromination is more selective than chlorination because the reaction is less exothermic. Most commonly bromination is conducted by the addition of Br2 to alkenes. An example of bromination is the organic synthesis of the anesthetic halothane from trichloroethylene:Synthesis of essential drugs, Ruben Vardanyan, Victor Hruby; Elsevier 2005 :Halothane synthesis Organobromine compounds are the most common organohalides in nature. Their formation is catalyzed by the enzyme bromoperoxidase which utilizes bromide in combination with oxygen as an oxidant.
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32) reported first in the years 1838 to 1839 on the compound as reaction product of anhydrous ethanol and anhydrous sulfuric acid. Carbyl sulfate is produced in the highly exothermic (about 800 kcal/kg) reaction of ethylene and sulfur trioxide in the vapor phase in nearly quantitative yield. : Carbyl sulfate synthesis Disulfuric acid and chlorosulfuric acid can also be used as a sulfonating agent, replacing sulfur trioxide. Instead of ethylene, ethylene- forming agents can be used, e.g.
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Nitromethane is produced industrially by combining propane and nitric acid in the gas phase at 350–450 °C (662–842 °F). This exothermic reaction produces the four industrially significant nitroalkanes: nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane. The reaction involves free radicals, including the alkoxyl radicals of the type CH3CH2CH2O, which arise via homolysis of the corresponding nitrite ester. These alkoxy radicals are susceptible to C—C fragmentation reactions, which explains the formation of a mixture of products.
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As with the other parameters, the required precision of temperature control depends upon the process specification. The autoclave should exceed this capability by a margin sufficient to preclude all chances of inadequate or excessive temperatures in the workload. Too hot and the parts can be damaged or undergo thermal excursion;Some resin systems are vulnerable to exothermic heating; in extreme cases, this can cause fires inside the autoclave. too cold and the full structural properties may not be realized.
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Since many common substances catalyze peroxide's exothermic decomposition into steam and oxygen, handling of HTP requires special care and equipment. It is noted that the common materials iron and copper are incompatible with peroxide, but the reaction can be delayed for seconds or minutes, depending on the grade of peroxide used. Small hydrogen peroxide spills are easily dealt with by flooding the area with water. Not only does this cool any reacting peroxide but it also dilutes it thoroughly.
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Such engines were used on the Viking program landers in the 1970s as well as the Phoenix lander and Curiosity rover which landed on Mars in May 2008 and August 2012, respectively. In all hydrazine monopropellant engines, the hydrazine is passed over a catalyst such as iridium metal supported by high-surface-area alumina (aluminium oxide), which causes it to decompose into ammonia, nitrogen gas, and hydrogen gas according to the following reactions: 1) N2H4 -> N2 + 2H2 2) 3N2H4 -> 4 NH3 + N2 3) 4NH3 + N2H4 -> 3 N2 + 8 H2 The first two reactions are extremely exothermic (the catalyst chamber can reach 800°C in a matter of milliseconds,) and they produce large volumes of hot gas from a small volume of liquid, making hydrazine a fairly efficient thruster propellant with a vacuum specific impulse of about 220 seconds. Reaction 2 is the most exothermic, but produces a smaller number of molecules than that of reaction 1. Reaction 3 is endothermic and reverts the effect of reaction 2 back to the same effect as reaction 1 alone (lower temperature, greater number of molecules).
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Applying the Gibbs energy equation for reactions: :\Delta G = \Delta H - T\Delta S General thermodynamics states that for spontaneous reactions at constant temperature and pressure, the change in free energy should be negative. Since a free particle is restrained to a surface, and unless the surface atom is highly mobile, entropy is lowered. This means that the enthalpy term must be negative, implying an exothermic reaction. Figure 1 is a graph of physisorption and chemisorption energy curves of tungsten and oxygen.
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Potassium nitrate can be made by combining ammonium nitrate and potassium hydroxide. :NH4NO3 (aq) + KOH (aq) → NH3 (g) + KNO3 (aq) + H2O (l) An alternative way of producing potassium nitrate without a by-product of ammonia is to combine ammonium nitrate, found in instant ice packs, and potassium chloride, easily obtained as a sodium-free salt substitute. :NH4NO3 (aq) + KCl (aq) → NH4Cl (aq) + KNO3 (aq) Potassium nitrate can also be produced by neutralizing nitric acid with potassium hydroxide. This reaction is highly exothermic.
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Charente, France. Sizes of stacks of baled hay need to be carefully managed, as the curing process is exothermic and the built up heat around internal bales can reach ignition temperatures in the right weather history and atmospheric conditions. Building a deep stack either too wide, or too high increases the risk of spontaneous ignition. Rectangular bales are easier to transport than round bales, since there is little risk of the bale rolling off the back of a flatbed trailer.
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Traditional Fenton's reagent applications can be very exothermic when significant iron, manganese or contaminant (i.e. NAPL concentrations) are present in an injection zone. Over the course of the reaction, the groundwater heats up and, in some cases, reagent and vapors can surface out of the soil. Stabilizing the peroxide can significantly increase the residence time and distribution of the reagent while reducing the potential for excessive temperatures by effectively isolating the peroxide from naturally occurring divalent transition metals in the treatment zone.
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Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. Some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. Understanding chemical changes is a major part of the science of chemistry.
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Since the products are higher in energy, the transition state appears to be right before the reaction is complete. One other useful interpretation of the postulate often found in textbooks of organic chemistry is the following: :Assume that the transition states for reactions involving unstable intermediates can be closely approximated by the intermediates themselves. This interpretation ignores extremely exothermic and endothermic reactions which are relatively unusual and relates the transition state to the intermediates which are usually the most unstable.
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In these tests, the samples are isothermally or non-isothermally heated and once exothermic heat is detected, OIT or OOT measurements are determined. In order to keep the duration of the tests short (under 2 hours), the testing temperature is raised above 180 °C. Basically, the test sample is heated then maintained at constant temperature for some time to stabilize. Oxygen/air is then applied and the time of application to beginning of oxidation is the “oxidation induction time” (OIT).
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The aromatic ring of phenol is activated towards electrophilic substitution reactions, and attempted nitration of phenol, even with dilute nitric acid, results in the formation of high molecular weight tars. In order to minimize these side reactions, anhydrous phenol is sulfonated with fuming sulfuric acid, and the resulting p-hydroxyphenylsulfonic acid is then nitrated with concentrated nitric acid. During this reaction, nitro groups are introduced, and the sulfonic acid group is displaced. The reaction is highly exothermic, and careful temperature control is required.
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Electronic components are sometimes encased in silicone to increase stability against mechanical and electrical shock, radiation and vibration, a process called "potting". Silicones are used where durability and high performance are demanded of components under hard conditions, such as in space (satellite technology). They are selected over polyurethane or epoxy encapsulation when a wide operating temperature range is required (−65 to 315 °C). Silicones also have the advantage of little exothermic heat rise during cure, low toxicity, good electrical properties, and high purity.
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Since the products are higher in energy, the transition state appears to be right before the reaction is complete. One other useful interpretation of the postulate often found in textbooks of organic chemistry is the following: :Assume that the transition states for reactions involving unstable intermediates can be closely approximated by the intermediates themselves. This interpretation ignores extremely exothermic and endothermic reactions which are relatively unusual and relates the transition state to the intermediates which are usually the most unstable.
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Lost City is an exemplary location for the study of abiotic methanogenesis and hydrogenesis, as serpentinization reactions produce methane and hydrogen. Supplementing Fischer-Tropsch reactions; The reactions are exothermic and warm the surrounding waters via reaction heating, though fluid temperatures are still relatively low (40°–90 °C) when compared to other hydrothermal systems. Furthermore, local pH is increased to values of over 9, which enables calcium carbonate precipitation. Since serpentinization is particularly extensive, carbon dioxide concentrations are also very low.
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On an industrial scale, cyclohexane is produced by hydrogenation of benzene in the presence of a Raney nickel catalyst.Fred Fan Zhang, Thomas van Rijnman, Ji Soo Kim, Allen Cheng "On Present Methods of Hydrogenation of Aromatic Compounds, 1945 to Present Day" Lunds Tekniska Högskola 2008 Producers of cyclohexane account for approximately 11.4% of global demand for benzene. The reaction is highly exothermic, with ΔH(500 K) = -216.37 kJ/mol). Dehydrogenation commenced noticeably above 300 °C, reflecting the favorable entropy for dehydrogenation.
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Reduction of ZrO2 and HfO2 to their respective diborides can also be achieved via metallothermic reduction. Inexpensive precursor materials are used and reacted according to the reaction below: ZrO2 \+ B2O3 \+ 5Mg → ZrB2 \+ 5MgO Mg is used as a reactant in order to allow for acid leaching of unwanted oxide products. Stoichiometric excesses of Mg and B2O3 are often required during metallothermic reductions in order to consume all available ZrO2. These reactions are exothermic and can be used to produce the diborides by SHS.
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The dissolution of the different crystalline phases of calcium sulfate in water is exothermic and releases heat (decrease in Enthalpy: ΔH < 0). As an immediate consequence, to proceed, the dissolution reaction needs to evacuate this heat that can be considered as a product of reaction. If the system is cooled, the dissolution equilibrium will evolve towards the right according to the Le Chatelier principle and calcium sulfate will dissolve more easily. The solubility of calcium sulfate increases thus when the temperature decreases.
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Diagram of thermal runaway Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. It is a kind of uncontrolled positive feedback. In other words, "thermal runaway" describes a process which is accelerated by increased temperature, in turn releasing energy that further increases temperature. In chemistry (and chemical engineering), it is associated with strongly exothermic reactions that are accelerated by temperature rise.
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Note the minuscule broadening in the peak of the three-state protein's DSC curve, which may or may not appear statistically significant to the naked eye. The result of a DSC experiment is a curve of heat flux versus temperature or versus time. There are two different conventions: exothermic reactions in the sample shown with a positive or negative peak, depending on the kind of technology used in the experiment. This curve can be used to calculate enthalpies of transitions.
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DSC is widely used in the pharmaceutical and polymer industries. For the polymer chemist, DSC is a handy tool for studying curing processes, which allows the fine tuning of polymer properties. The cross-linking of polymer molecules that occurs in the curing process is exothermic, resulting in a negative peak in the DSC curve that usually appears soon after the glass transition. In the pharmaceutical industry it is necessary to have well- characterized drug compounds in order to define processing parameters.
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An automobile engine is called an internal combustion engine because it burns fuel (an exothermic chemical reaction) inside a cylinder and uses the expanding gases to drive a piston. A jet engine uses a turbine to compress air which is burned with fuel so that it expands through a nozzle to provide thrust to an aircraft, and so is also an "internal combustion engine." "Internal combustion engine", Concise Encyclopedia of Science and Technology, Third Edition, Sybil P. Parker, ed. McGraw-Hill, Inc.
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The simplest theory to predict the behaviour of detonations in gases is known as Chapman-Jouguet (CJ) theory, developed around the turn of the 20th century. This theory, described by a relatively simple set of algebraic equations, models the detonation as a propagating shock wave accompanied by exothermic heat release. Such a theory confines the chemistry and diffusive transport processes to an infinitesimally thin zone. A more complex theory was advanced during World War II independently by Zel'dovich, von Neumann, and W. Doering.
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Urea nitrate is a fertilizer-based high explosive that has been used in improvised explosive devices in Afghanistan, Pakistan, Iraq, and various other terrorist acts elsewhere in the world, like the 1993 World Trade Center bombings. It has a destructive power similar to better-known ammonium nitrate explosives, with a velocity of detonation between and . Urea nitrate is produced in one step by reaction of urea with nitric acid. This is an exothermic reaction, so steps must be taken to control the temperature.
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In practice, virtually all solid or liquid substances start to glow around , with a mildly dull red color, whether or not a chemical reaction takes place that produces light as a result of an exothermic process. This limit is called the Draper point. The incandescence does not vanish below that temperature, but it is too weak in the visible spectrum to be perceivable. At higher temperatures, the substance becomes brighter and its color changes from red towards white and finally blue.
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Its buckled structure gives silicene a tuneable band gap by applying an external electric field. Silicene's hydrogenation reaction is more exothermic than graphene's. Another difference is that since silicon's covalent bonds do not have pi- stacking, silicene does not cluster into a graphite-like form. The formation of a buckled structure in silicene unlike planar structure of graphene has been attributed to strong Pseudo Jahn-Teller distortions arising due to vibronic coupling between closely spaced filled and empty electronic states.
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Chloridizing roasting transforms certain metal compounds to chlorides, through oxidation or reduction. Some metals such as uranium, titanium, beryllium and some rare earths are processed in their chloride form. Certain forms of chloridizing roasting may be represented by the overall reactions: :2NaCl + MS + 2O2 -> Na2SO4 \+ MCl, :4NaCl + 2MO + S2 \+ 3O2 -> 2Na2SO4 \+ 2MCl2 The first reaction represents the chlorination of a sulfide ore involving an exothermic reaction. The second reaction involving an oxide ore is facilitated by addition of elemental sulfur.
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EMPA researchers are experimenting with concentrated sodium hydroxide (NaOH) as the thermal storage or seasonal reservoir medium for domestic space-heating. If water is added to solid or concentrated sodium hydroxide (NaOH), heat is released. The dilution is exothermic – chemical energy is released in the form of heat. Conversely, by applying heat energy into a dilute sodium hydroxide solution the water will evaporate so that the solution becomes more concentrated and thus stores the supplied heat as latent chemical energy.
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The chemical reaction that occurs when plaster is mixed with water is exothermic. When plaster sets, it can reach temperatures of more than 60 °C (140°F) and, in large volumes, can burn the skin. In January 2007, a secondary school student in Lincolnshire, England sustained third-degree burns after encasing her hands in a bucket of plaster as part of a school art project. The burns were so severe she required amputation of both her thumbs and six of her fingers.
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The mechanism of PEP carboxylase has been well studied. The enzymatic mechanism of forming oxaloacetate is very exothermic and thereby irreversible; the biological Gibbs free energy change (△G°’) is -30kJmol−1. The substrates and cofactor bind in the following order: metal cofactor (either Co2+, Mg2+, or Mn2+), PEP, bicarbonate (HCO3−). The mechanism proceeds in two major steps, as described below and shown in figure 2: Figure 2: the Phosphoenolpyruvate (PEP) carboxylase enzymatic mechanism converting bicarbonate and PEP to oxaloacetate and phosphate.
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The energy from this exothermic reaction is used to bind inorganic phosphates to ADP, which converts it to ATP, and convert NAD+ to NADH. The pyruvates break down into two acetaldehyde molecules and give off two carbon dioxide molecules as waste products. The acetaldehyde is reduced into ethanol using the energy and hydrogen from NADH, and the NADH is oxidized into NAD+ so that the cycle may repeat. The reaction is catalyzed by the enzymes pyruvate decarboxylase and alcohol dehydrogenase.
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Calcium hypochlorite is produced on an industrial scale and has good stability. Strontium hypochlorite, Sr(OCl)2, is not well characterised and its stability has not yet been determined. The hypochlorite ion is unstable with respect to disproportionation. Upon heating, it degrades to a mixture of chloride, oxygen, and other chlorates: :2 → 2 \+ :3 → 2 \+ This reaction is exothermic and in the case of concentrated hypochlorites, such as LiOCl and Ca(OCl)2, can lead to a dangerous thermal runaway and potentially explosions.
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For example, coal burns in a fireplace in the presence of oxygen, but it does not when it is stored at room temperature. The reaction is spontaneous at low and high temperatures but at room temperature its rate is so slow that it is negligible. The increase in temperature, as created by a match, allows the reaction to start and then it heats itself, because it is exothermic. That is valid for many other fuels, such as methane, butane, and hydrogen.
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Thus, it was said, quicklime (CaO) was apparently set ablaze when doused with cold water (an effect later explained as an exothermic reaction). It was also the understood reason for why water, such as that in wells, appeared warmer in winter than in summer (later explained as an example of sensory adaptation). It was also suggested that thunder and lightning were the results of antiperistasis caused by the coldness of the sky. Peripatetic philosophers, who were followers of Aristotle, made extensive use of the principle of antiperistasis.
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A device making use of exothermic chemical reactions designed to result in the rapid spread of fire for the purpose of creating a primary patho-physiological effect (morbidity and mortality), or secondary psychological effect (causing fear and behavior modification) on a larger population or it may be used with the intent of gaining a tactical advantage. Such devices may be fabricated in a completely improvised manner or may be an improvised modification to an existing weapon. A common type of this is the Molotov cocktail.
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Bags of cement routinely have health and safety warnings printed on them because not only is cement highly alkaline, but the setting process is exothermic. As a result, wet cement is strongly caustic (pH = 13.5) and can easily cause severe skin burns if not promptly washed off with water. Similarly, dry cement powder in contact with mucous membranes can cause severe eye or respiratory irritation. Some trace elements, such as chromium, from impurities naturally present in the raw materials used to produce cement may cause allergic dermatitis.
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Ethylene production by steam cracking consumes large amounts of energy and uses oil and natural gas fractions such as naphtha and ethane. The oxidative coupling of methane to ethylene is written below:Olah, G., Molnar, A. “Hydrocarbon Chemistry” John Wiley & Sons, New York, 2003. . : 2 + -> \+ 2 The reaction is exothermic (∆H = -280 kJ/mol) and occurs at high temperatures (750–950 ˚C). In the reaction, methane () is activated heterogeneously on the catalyst surface, forming methyl free radicals, which then couple in the gas phase to form ethane ().
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On an industrial scale, diallyl disulfide is produced from sodium disulfide and allyl bromide or allyl chloride at temperatures of 40–60 °C in an inert gas atmosphere; sodium disulfide is generated in situ by reacting sodium sulfide with sulfur. The reaction is exothermic and its theoretical efficiency of 88% has been achieved in practice. WIPO Patent WO/2006/16881 :500px Smaller quantities can be synthesized from the same starting materials, but in air and using tetrabutylammonium bromide as a catalyst. The corresponding yield is below 82%.
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255–271; On the laboratory scale, PhF is prepared by the thermal decomposition of the benzenediazonium tetrafluoroborate: :PhN2BF4 -> PhF + BF3 \+ N2 According to the procedure, solid [PhN2]BF4 is heated with a flame to initiate an exothermic reaction, which also affords boron trifluoride and nitrogen gas. Product PhF and BF3 are readily separated because of their differing boiling points.. The technical synthesis is by the reaction of cyclopentadiene with difluorocarbene. The initially formed cyclopropane undergoes a ring expansion and subsequent elimination of hydrogen fluoride.
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Thermometric titrimetry offers a rapid, highly precise method for the determination of aluminium in solution. A solution of aluminium is conditioned with acetate buffer and an excess of sodium and potassium ions. Titration with sodium or potassium fluoride yields the exothermic precipitation of an insoluble alumino-fluoride salt. : Al3+ \+ Na+ \+ 2K+ \+ 6F− ↔ K2NaAlF6↓ Because 6 mole of fluoride react with one mole of aluminium, the titration is particularly precise, and a coefficient of variance (CV) of 0.03 has been achieved in the analysis of alum.
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Instead, the new bond can shed its excess energy - by radiation, by transfer to other motions in the molecule, or to other molecules through collisions - and then become a stable new bond. This excess energy is the heat that leaves the molecular system. Uncontrolled exothermic reactions, those leading to fires and explosions, are wasteful because it is difficult to capture the released energy. Nature effects combustion reactions under highly controlled conditions, avoiding fires and explosions, in aerobic respiration so as to capture the released energy, e.g.
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During a meltdown, the temperature of the fuel rods increases and they can deform, in the case of zircaloy cladding, above . If the reactor pressure is low, the pressure inside the fuel rods ruptures the control rod cladding. High-pressure conditions push the cladding onto the fuel pellets, promoting formation of uranium dioxide–zirconium eutectic with a melting point of . An exothermic reaction occurs between steam and zirconium, which may produce enough heat to be self-sustaining without the contribution of decay heat from radioactivity.
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It was also observed that the adsorption process of BPA on sediment is exothermic, the molar formation enthalpy, ΔH°, was negative, the free energy ΔG°, was negative, and the molar entropy, ΔS°, was positive. This indicates that the adsorption of BPA is driven by enthalpy. The adsorption of BPA has also been observed to decrease with increasing pH. A 2005 study conducted in the United States had found that 91–98% of BPA may be removed from water during treatment at municipal water treatment plants.
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Aluminium as a metal fuel with oxidizers creates highly exothermic reactions. When Al2O3 is added to a pressure system, the reaction goes from steady, to accelerating, to unstable. This reaction indicates that unstable intermediates such as AlO or Al2O condense or do not form, which prevent acceleration and convection down the pressure system.Malchi, J. Y., Yetter, R. A., Foley, T. J., Son, S. F. “The effect of added Al2O3 on the propagation behavior of an Al/CuO nanoscale thermite.” Combustion Science and Technology. 180 (2008):1278-1294.
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Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from lithium using one of the following reactions: : + → + : + → + + The reactant neutron is supplied by the D-T fusion reaction shown above, and the one that has the greatest yield of energy. The reaction with 6Li is exothermic, providing a small energy gain for the reactor. The reaction with 7Li is endothermic but does not consume the neutron. At least some neutron multiplication reactions are required to replace the neutrons lost to absorption by other elements.
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Fusion reactions occur when two or more atomic nuclei come close enough for long enough that the nuclear force pulling them together exceeds the electrostatic force pushing them apart, fusing them into heavier nuclei. For nuclei lighter than iron-56, the reaction is exothermic, releasing energy. For nuclei heavier than iron-56, the reaction is endothermic, requiring an external source of energy. Hence, nuclei smaller than iron-56 are more likely to fuse while those heavier than iron-56 are more likely to break apart.
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Not all supernovae are triggered by runaway nuclear fusion. Type Ib, Ic and type II supernovae also undergo core collapse, but because they have exhausted their supply of atomic nuclei capable of undergoing exothermic fusion reactions, they collapse all the way into neutron stars, or in the higher-mass cases, stellar black holes, powering explosions by the release of gravitational potential energy (largely via release of neutrinos). It is the absence of runaway fusion reactions that allows such supernovae to leave behind compact stellar remnants.
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Self-heating cans have dual chambers, one surrounding the other. In one version, the inner chamber holds the food or drink, and the outer chamber houses chemicals which undergo an exothermic reaction when combined. When the user wants to heat the contents of the can, a ring on the can—when pulled—breaks the barrier which keeps the chemicals in the outer chamber apart from the water. In another type, the chemicals are in the inner chamber and the beverage surrounds it in the outer chamber.
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Because of historical accident, students encounter a source of possible confusion between the terminology of physics and biology. Whereas the thermodynamic terms "exothermic" and "endothermic" respectively refer to processes that give out heat energy and processes that absorb heat energy, in biology the sense is effectively inverted. The metabolic terms "ectothermic" and "endothermic" respectively refer to organisms that rely largely on external heat to achieve a full working temperature, and to organisms that produce heat from within as a major factor in controlling their bodily temperature.
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For the hydration of alkenes, the general chemical equation of the reaction is the following: :RRC=CH2 in H2O/acid → RRC(OH)-CH3 A hydroxyl group (OH−) attaches to one carbon of the double bond, and a proton (H+) adds to the other carbon of the double bond. The reaction is highly exothermic. In the first step, the alkene acts as a nucleophile and attacks the proton, following Markovnikov's rule. In the second step an H2O molecule bonds to the other, more highly substituted carbon.
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The two nuclei in a dihydrogen molecule can have two different spin states. Parahydrogen, in which the two nuclear spins are antiparallel, is more stable than orthohydrogen, in which the two are parallel. At room temperature, gaseous hydrogen is mostly in the ortho isomeric form due to thermal energy, but an ortho-enriched mixture is only metastable when liquified at low temperature. It slowly undergoes an exothermic reaction to become the para isomer, with enough energy released as heat to cause some of the liquid to boil.
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Pure sodium hydroxide is a colorless crystalline solid that melts at without decomposition, and with a boiling point of . It is highly soluble in water, with a lower solubility in polar solvents such as ethanol and methanol. NaOH is insoluble in ether and other non-polar solvents. Similar to the hydration of sulfuric acid, dissolution of solid sodium hydroxide in water is a highly exothermic reaction where a large amount of heat is liberated, posing a threat to safety through the possibility of splashing.
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Because of historical accident, students encounter a source of possible confusion between the terminology of physics and biology. Whereas the thermodynamic terms "exothermic" and "endothermic" respectively refer to processes that give out heat energy and processes that absorb heat energy, in biology the sense is effectively reversed. The metabolic terms "ectotherm" and "endotherm" respectively refer to organisms that rely largely on external heat to achieve a full working temperature, and to organisms that produce heat from within as a major factor in controlling their body temperatures.
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A plot of IMC data for a generic exothermic rate process in a sealed ampoule in which the process (and thus the heat flow) begins, accelerates, reaches a peak and then subsides. Below the heat flow plot is a plot showing integration of the heat flow data to give accumulated heat vs. time. As illustrated graphically, the lag phase duration and maximum heat generation rate (growth rate) can be calculated from the integrated data (after Howell, et al. 2011. Used with publisher permission). Fig.
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The formation of this may be affected by pH and temperature but is most strongly effected by the geometry of the substrate, with cis-diols reacting significantly faster than trans-diols. The reactions are exothermic and are typically performed at 0 °C. As periodate salts are only readily soluble in water reactions are generally performed in aqueous media. Where solubility is an issue periodic acid may be used, as this is soluble in alcohols; phase transfer catalysts are also effective in biphasic reaction mixtures.
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When the wrap is removed from its sealed pouch and exposed to oxygen, the disks oxidize, producing an exothermic reaction. When this product was applied to the low back muscles, it provided greater pain relief for 24 hours after application when compared to ibuprofen, acetaminophen, and no treatment. When the same product was applied to the wrist, it decreased pain and improved range of motion (ROM) in patients experiencing wrist pain. Scientists have tested the ability of these topical wraps to increase paraspinal muscle temperatures.
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The bombardier beetle has a device which allows it to shoot corrosive and foul-smelling bubbles at its enemies. The beetle produces and stores hydroquinone and hydrogen peroxide, in two separate reservoirs in the rear tip of its abdomen. When threatened, the beetle contracts muscles that force the two reactants through valved tubes into a mixing chamber containing water and a mixture of catalytic enzymes. When combined, the reactants undergo a violent exothermic chemical reaction, raising the temperature to near the boiling point of water.
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The conventional Claus process described above is limited in its conversion due to the reaction equilibrium being reached. Like all exothermic reactions, greater conversion can be achieved at lower temperatures, however as mentioned the Claus reactor must be operated above the sulfur dew point (120–150 °C) to avoid liquid sulfur physically deactivating the catalyst. To overcome this problem, the sub dew point Clauss reactors are oriented in parallel, with one operating and one spare. When one reactor has become saturated with adsorbed sulfur, the process flow is diverted to the standby reactor.
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Via the water-gas shift reaction, additional hydrogen can be obtained by treating the carbon monoxide generated by steam reforming with water: :CO + H2O ⇌ CO2 \+ H2 This reaction is mildly exothermic (produces heat, ΔHr= -41 kJ/mol). The United States produces 9—10 million tons of hydrogen per year, mostly with steam reforming of natural gas. The worldwide ammonia production, using hydrogen derived from steam reforming, was 144 million tonnes in 2014. The energy consumption has been reduced from 100 GJ/tonne of ammonia in 1920, to 27 GJ by 2019.
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ZrB2 can be synthesized by stoichiometric reaction between constituent elements, in this case Zr and B. This reaction provides for precise stoichiometric control of the materials. At 2000 K, the formation of ZrB2 via stoichiometric reaction is thermodynamically favorable (ΔG=−279.6 kJ mol−1) and therefore, this route can be used to produce ZrB2 by self- propagating high-temperature synthesis (SHS). This technique takes advantage of the high exothermic energy of the reaction to cause high temperature, fast combustion reactions. Advantages of SHS include higher purity of ceramic products, increased sinterability, and shorter processing times.
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The First Law of Thermodynamics is a statement of the conservation of energy; though it can be changed from one form to another, energy can be neither created nor destroyed. From the first law, a principle called Hess's Law arises. Hess’s Law states that the heat absorbed or evolved in a given reaction must always be constant and independent of the manner in which the reaction takes place. Although some intermediate reactions may be endothermic and others may be exothermic, the total heat exchange is equal to the heat exchange had the process occurred directly.
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Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. Fire is hot because the conversion of the weak double bond in molecular oxygen, O2, to the stronger bonds in the combustion products carbon dioxide and water releases energy (418 kJ per 32 g of O2); the bond energies of the fuel play only a minor role here. At a certain point in the combustion reaction, called the ignition point, flames are produced. The flame is the visible portion of the fire.
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Reactive multi-layer foils are a class of reactive materials, sometimes referred to as a pyrotechnic initiator of two mutually reactive metals, sputtered to form thin layers that create a laminated foil. On initiation by a heat pulse, delivered by a bridge wire, a laser pulse, an electric spark, a flame, or by other means, the metals undergo self-sustaining exothermic reaction, producing an intermetallic compound. The reaction occurs in solid and liquid phase only, without releasing any gas. One particular type of such materials is aluminum-nickel multilayered foil, that produces (NiAl).
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At the high temperatures and pressures found at depth within the Earth the olivine structure is no longer stable. Below depths of about olivine undergoes an exothermic phase transition to the sorosilicate, wadsleyite and, at about depth, wadsleyite transforms exothermically into ringwoodite, which has the spinel structure. At a depth of about , ringwoodite decomposes into silicate perovskite ((Mg,Fe)SiO3) and ferropericlase ((Mg,Fe)O) in an endothermic reaction. These phase transitions lead to a discontinuous increase in the density of the Earth's mantle that can be observed by seismic methods.
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Pyrite oxidation is sufficiently exothermic that underground coal mines in high- sulfur coal seams have occasionally had serious problems with spontaneous combustion in the mined-out areas of the mine. The solution is to hermetically seal the mined-out areas to exclude oxygen. In modern coal mines, limestone dust is sprayed onto the exposed coal surfaces to reduce the hazard of dust explosions. This has the secondary benefit of neutralizing the acid released by pyrite oxidation and therefore slowing the oxidation cycle described above, thus reducing the likelihood of spontaneous combustion.
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Copper(II) chloride is prepared commercially by the action of chlorination of copper. Copper at red heat (300-400°C) combines directly with chlorine gas, giving (molten) copper (II) chloride. The reaction is very exothermic. : Cu(s) + Cl2(g) → CuCl2(l) It is also commercially practical to combine copper(II) oxide with an excess of ammonium chloride at similar temperatures, producing copper chloride, ammonia, and water: : CuO + 2NH4Cl → CuCl2 \+ 2NH3 \+ H2O Although copper metal itself cannot be oxidised by hydrochloric acid, copper- containing bases such as the hydroxide, oxide, or copper(II) carbonate can be.
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Fluorine has two solid forms, α- and β-fluorine. The latter crystallizes at −220 °C (−364 °F) and is transparent and soft, with the same disordered cubic structure of freshly crystallized solid oxygen, unlike the orthorhombic systems of other solid halogens. Further cooling to −228 °C (−378 °F) induces a phase transition into opaque and hard α-fluorine, which has a monoclinic structure with dense, angled layers of molecules. The transition from β- to α-fluorine is more exothermic than the condensation of fluorine, and can be violent..
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1988 The parameters that are measured are referred to as the glass transition value (Tg) and melting temperature (Tm). These values are measured over time and are comparable between an inert reference sample and the analyte. Changes in the (Tm) and (Tg) values evaluate phase changes (solid, liquid-gel, liquid, etc.) in which an endothermic or exothermic process occurs. This technique is useful for monitoring the phase changes in phospholipids by providing information such as the amount of heat released or absorbed and time for phase transitions to occur, etc.
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This exothermic reaction helps to heat the LLSVP, but it is not sufficient enough to account for the total energy needed to sustain it. So it is hypothesized that the material from the slab graveyard can become extremely dense and form large pools of melt concentrate enriched in uranium, thorium, and potassium. These concentrated radiogenic elements are thought to provide the high temperatures needed. So, the appearance and disappearance of slab graveyards predicts the birth and death of an LLSVP, potentially changing the dynamics of all plate tectonics.
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Pharaoh's serpent demonstration Mercury thiocyanate was formerly used in pyrotechnics causing an effect known as the Pharaoh's serpent or Pharaoh's snake. When the compound is in the presence of a strong enough heat source, a rapid, exothermic reaction that produces a large mass of coiling, serpent-like solid is started. An inconspicuous flame, which is often blue but can also be yellow/orange, accompanies the combustion. The resulting solid can range from dark graphite gray to light tan in color with the inside generally much darker than the outside.
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In the ANG process, natural gas adsorbs to a porous adsorbent at relatively low pressure (100 to 900 psi) and ambient temperature, solving both the high-pressure and low- temperature problems. If a suitable adsorbent is used, it is possible to store more gas in an adsorbent-filled vessel than in an empty vessel at the same pressure. The amount of adsorbed gas depends on pressure, temperature and adsorbent type. Since this adsorption process is exothermic, an increase in pressure or a decrease in temperature enhances the efficiency of the adsorption process.
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This is a thermodynamic argument, and kinetics are ignored. As determined by the enthalpies below the corresponding molecules, the enthalpy of reaction for 2-methyl-1-butene going to 2-methyl-butane is −29.07 kcal/mol, which is in great agreement with the value calculated from NIST, −28.31 kcal/mol. For 2-butanone going to 2-butanol, enthalpy of reaction is −13.75 kcal/mol, which again is in excellent agreement with −14.02 kcal/mol. While both reactions are thermodynamically favored, the alkene will be far more exothermic than the corresponding ketone.
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Thus, the base hydrolysis route will afford the carboxylate (or the amide contaminated with the carboxylate). On the other hand, the acid catalyzed reactions requires a careful control of the temperature and of the ratio of reagents in order to avoid the formation of polymers, which is promoted by the exothermic character of the hydrolysis. The classical procedure to convert a nitrile to the corresponding primary amide calls for adding the nitrile to cold concentrated sulfuric acid. The further conversion to the carboxylic acid is disfavored by the low temperature and low concentration of water.
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These are highly exothermic reactions. Russell demonstrated that alkaline vents created an abiogenic proton motive force (PMF) chemiosmotic gradient, in which conditions are ideal for an abiogenic hatchery for life. Their microscopic compartments "provide a natural means of concentrating organic molecules," composed of iron-sulfur minerals such as mackinawite, endowed these mineral cells with the catalytic properties envisaged by Günter Wächtershäuser. This movement of ions across the membrane depends on a combination of two factors: # Diffusion force caused by concentration gradient—all particles including ions tend to diffuse from higher concentration to lower.
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A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere- transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage, and explosion-generated effects. Bombs have been utilized since the 11th century starting in East Asia. The term bomb is not usually applied to explosive devices used for civilian purposes such as construction or mining, although the people using the devices may sometimes refer to them as a "bomb".
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A reaction with a negative Q value is endothermic, i.e. requires a net energy input, since the kinetic energy of the final state is less than the kinetic energy of the initial state. Observe that a chemical reaction is exothermic when it has a negative enthalpy of reaction, in contrast a positive Q value in a nuclear reaction. The Q value can also be expressed in terms of the binding energies of the nuclear species as: Q=B_f- B_i Proof: Note that the count of nucleons is conserved in a nuclear reaction.
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The formation of a crystal lattice is exothermic, i.e., the value of ΔHlattice is negative because it corresponds to the coalescing of infinitely separated gaseous ions in vacuum to form the ionic lattice. Sodium chloride crystal lattice The concept of lattice energy was originally developed for rocksalt-structured and sphalerite-structured compounds like NaCl and ZnS, where the ions occupy high-symmetry crystal lattice sites. In the case of NaCl, lattice energy is the energy released by the reaction : Na+ (g) + Cl− (g) -> NaCl (s) which would amount to -786 kJ/mol.
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When these packs are exposed to air, an exothermic chemical reaction occurs, which provides several hours of heat. Another chemical heating pad uses a gel that can be activated by twisting the package, thus triggering a chemical reaction. The pack can be put in a pot of boiling water to convert the chemical reaction back and allow it to be reused. While these products are commonly called "hand warmers", they can be placed in boots or, with special garments such as vests, in cloth pockets on the inside of the garment.
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It also has a strong tendency to cause corrosion, rusting the steel used in most vehicles and the rebar in concrete bridges. Depending on the concentration, it can be toxic to some plants and animals, and some urban areas have moved away from it as a result. More recent snowmelters use other salts, such as calcium chloride and magnesium chloride, which not only depress the freezing point of water to a much lower temperature, but also produce an exothermic reaction. They are somewhat safer for sidewalks, but excess should still be removed.
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This coal is also amongst the world's 'wettest' coal, with a typical moisture content of 60 per cent water by weight. High moisture content makes Victorian brown coal an inefficient fuel source and is the primary reason why the Hazelwood power station in the Latrobe Valley is regarded as the world's dirtiest coal-fired power station. The Coldry Process uses low- pressure mechanical shear to create a natural exothermic reaction within the coal that then naturally expels 80 per cent of the moisture content. Expelled moisture is then captured and recovered as distilled water.
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On thermal decomposition the alkali perchloratoborate salts form an alkali perchlorate, and boron trioxide as a solid residue, and gas containing dichlorine heptoxide, chlorine dioxide, chlorine, and oxygen. :2 M[B(ClO4)4] → 2 MClO4 \+ B2O3 \+ (3 Cl2O7 or 6 ClO2 \+ O2 or 6 Cl2 \+ O2) When the alkali perchloratoborates first start to decompose at the lower temperatures, the reaction is endothermic, and dichlorine heptoxide is formed. However, if caesium perchloratoborate is heated the decomposition becomes exothermic above 90 °C, and at 100 °C it explodes exothermically forming chlorine and oxygen.
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To be active α-Fe2O3 must be reduced to Fe and CrO3 must be reduced to Cr in presence of H2. This usually happens in the reactor start-up phase and because the reduction reactions are exothermic the reduction should happen under controlled circumstances. The lifetime of the iron-chrome catalyst is approximately 3–5 years, depending on how the catalyst is handled. Even though the mechanism for the HTS catalyst has been done a lot of research on, there is no final agreement on the kinetics/mechanism.
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The process is a low-pressure process that uses a Cu/ZnO/Al2O3 catalyst where copper is the active material. This catalyst is actually the same that the low-temperature shift catalyst in the WGS reaction is using. The reaction described below is carried out at 250 °C and 5-10 MPa: Both of these reactions are exothermic and proceeds with volume contraction. Maximum yield of methanol is therefore obtained at low temperatures and high pressure and with use of a catalyst that has a high activity at these conditions.
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The solubility of a given solute in a given solvent is function of temperature. Depending on the change in Gibbs free energy (ΔG) of the dissolution reaction, i.e., on the endothermic (ΔG > 0) or exothermic (ΔG < 0) character of the dissolution reaction, the solubility of a given compound may increase or decrease with temperature. The van 't Hoff equation relates the change of solubility equilibrium constant (Ksp) to temperature change and to reaction enthalpy change (ΔH). For most solids and liquids, their solubility increases with temperature because their dissolution reaction is endothermic (ΔG > 0).
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This is also the case for calcium hydroxide (portlandite), whose solubility at 70 °C is about half of its value at 25 °C. The dissolution of calcium hydroxide in water is also an exothermic process (ΔG < 0) and obeys the van 't Hoff equation and Le Chatelier's principle. A lowering of temperature favors the removal of dissolution heat from the system and thus favors dissolution of Ca(OH)2: so portlandite solubility increases at low temperature. This temperature dependence is sometimes referred to as "retrograde" or "inverse" solubility.
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The fusion of two nuclei that create larger nuclei with lower atomic numbers than iron and nickel—a total nucleon number of about 60—is usually an exothermic process that releases more energy than is required to bring them together. It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the binding energy per nucleon in the nucleus begins to decrease. That means fusion processes producing nuclei that have atomic numbers higher than about 26, and atomic masses higher than about 60, is an endothermic process.
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Computational analysis of this compound suggests valence isomerization to biphenyl is very exothermic but also with a high kinetic barrier.Dehydro[12]annulenes: Structures, Energetics, and Dynamic Processes Lawrence A. Januar, Vivian Huynh, Taylor S. Wood, Claire Castro, and William L. Karney J. Org. Chem., 2011, 76 (2), pp 403–407 [14]annulyne was reported in 1962 by Jackman et al.The Nuclear Magnetic Resonance Spectroscopy of a Series of Annulenes and Dehydro-annulenes L. M. Jackman, F. Sondheimer, Y. Amiel, D. A. Ben-Efraim, Y. Gaoni, R. Wolovsky, A. A. Bothner-By J. Am. Chem. Soc.
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Likewise, as the sample undergoes exothermic processes (such as crystallization) less heat is required to raise the sample temperature. By observing the difference in heat flow between the sample and reference, differential scanning calorimeters are able to measure the amount of heat absorbed or released during such transitions. DSC may also be used to observe more subtle physical changes, such as glass transitions. It is widely used in industrial settings as a quality control instrument due to its applicability in evaluating sample purity and for studying polymer curing.
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Ethylene oxide is relatively stable to heating – in the absence of a catalyst, it does not dissociate up to , and only above there is a major exothermic decomposition, which proceeds through the radical mechanism. The first stage involves isomerization, however high temperature accelerates the radical processes. They result in a gas mixture containing acetaldehyde, ethane, ethyl, methane, hydrogen, carbon dioxide, ketene and formaldehyde. High-temperature pyrolysis () at elevated pressure in an inert atmosphere leads to a more complex composition of the gas mixture, which also contains acetylene and propane.
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The Boudouard reaction, named after Octave Leopold Boudouard, is the redox reaction of a chemical equilibrium mixture of carbon monoxide and carbon dioxide at a given temperature. It is the disproportionation of carbon monoxide into carbon dioxide and graphite or its reverse:Bioenergylist.org – Boudouard Reaction spreadsheet ::2CO + C Standard enthalpy of the Boudouard reaction at various temperatures The Boudouard reaction to form carbon dioxide and carbon is exothermic at all temperatures. However, the standard enthalpy of the Boudouard reaction becomes less negative with increasing temperature,Reaction Web as shown to the side.
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This theory, now known as ZND theory, admits finite-rate chemical reactions and thus describes a detonation as an infinitesimally thin shock wave followed by a zone of exothermic chemical reaction. With a reference frame of a stationary shock, the following flow is subsonic, so that an acoustic reaction zone follows immediately behind the lead front, the Chapman-Jouguet condition. Continued in Continued in There is also some evidence that the reaction zone is semi- metallic in some explosives. Both theories describe one-dimensional and steady wave fronts.
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When used in explosive devices, the main cause of damage from a detonation is the supersonic blast front (a powerful shock wave) in the surrounding area. This is a significant distinction from deflagrations where the exothermic wave is subsonic and maximum pressures are at most one eighth as great. Therefore, detonation is a feature for destructive purpose while deflagration is favored for the acceleration of firearms' projectiles. However, detonation waves may also be used for less destructive purposes, including deposition of coatings to a surface or cleaning of equipment (e.g.
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This limits its application to protected environments or short-term uses such as prototyping. Exposed to free air, KCl optics will "rot". Whereas KCl components were formerly used for infrared optics, it has been entirely replaced by much tougher crystals such as zinc selenide. Potassium chloride has also been used to produce heat packs which employ exothermic chemical reactions, but these have mostly been discontinued with the advent of cheaper and more efficient methods, such as the oxidation of metals ('Hot Hands' one-time-use products) or the crystallization of sodium acetate (multiple-use products).
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A reaction with ∆H°<0 is called exothermic reaction while one with ∆H°>0 is endothermic. Figure 8: Reaction Coordinate Diagrams showing favorable or unfavorable and slow or fast reactions The relative stability of reactant and product does not define the feasibility of any reaction all by itself. For any reaction to proceed, the starting material must have enough energy to cross over an energy barrier. This energy barrier is known as activation energy (∆G≠) and the rate of reaction is dependent on the height of this barrier.
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But when a peroxide is in a more pure form, the heat evolved by its decomposition may not dissipate as quickly as it is generated, which can result in increasing temperature, which further intensifies the rate of exothermic decomposition. This can create a dangerous situation known as a self-accelerating decomposition. A self-accelerating decomposition occurs when the rate of peroxide decomposition is sufficient to generate heat at a faster rate than it can be dissipated to the environment. Temperature is the main factor in the rate of decomposition.
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Firing the pellet oxidizes the magnetite (Fe3O4) to hematite (Fe2O3), an exothermic reaction that reduces the cost of pelletizing the concentrate. E. W. Davis of the University of Minnesota Mines Experiment Station is credited with developing the pelletizing process. Since the commercial development of this process in the Lake Superior region in the 1950s, the term "taconite" has been used globally to refer to iron ores amenable to upgrading by similar processes. Major producers of iron ore pellets from taconite in North America include Iron Ore Company of Canada, Cliffs Natural Resources, Inc.
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This reaction is highly exothermic and carries with it the risk of a runaway reaction leading to an explosion. In the laboratory, 2,4,6-trinitrotoluene is produced by a two-step process. A nitrating mixture of concentrated nitric and sulfuric acids is used to nitrate toluene to a mixture of mono- and di-nitrotoluene isomers, with careful cooling to maintain temperature. The nitrated toluenes are then separated, washed with dilute sodium bicarbonate to remove oxides of nitrogen, and then carefully nitrated with a mixture of fuming nitric acid and sulfuric acid.
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Some applications also use platinum-silver alloy; other bridgewire materials in use are platinum, gold, silver, tungsten, etc. Care has to be taken when selecting the material as it is in direct contact with the pyrotechnic composition and should not undergo corrosion in such conditions. Another material, able to actively release chemical energy, is Pyrofuze, aluminium wire clad with palladium; when being heated it undergoes strongly exothermic reaction as the molten metals form an alloy. A variant with the same function consists of laminated thin alternate layers of aluminium and nickel.
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Increasing the temperature also speeds up the reaction, but temperatures of 300 °C and above must be avoided, because they cause insoluble thorium pyrophosphate to form. Since dissolution is very exothermic, the monazite sand cannot be added to the acid too quickly. Conversely, at temperatures below 200 °C the reaction does not go fast enough for the process to be practical. To ensure that no precipitates form to block the reactive monazite surface, the mass of acid used must be twice that of the sand, instead of the 60% that would be expected from stoichiometry.
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The carbonization of wood in an industrial setting usually requires a temperature above 280 °C, which liberates energy and hence this reaction is said to be exothermic. This carbonization, which can also be seen as a spontaneous breakdown of the wood, continues until only the carbonised residue called charcoal remains. Unless further external heat is provided, the process stops and the temperature reaches a maximum of about 400 °C. This charcoal, however, will still contain appreciable amounts of tarry residue, together with the ash of the original wood.
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In theory the simplest means of producing furazan is the cyclic- dehydration of glyoxime (the di-oxime of glyoxal), however the instability of furazan to high temperature or extremes of pH requires that this process be performed carefully. The formation of furazan from glyoxime is also exothermic and takes place with the copious evolution of noxious gases. The reaction may be achieved by heating glyoxime to 150 °C in the presence of succinic anhydride; furazan will evaporate at this temperature and thus is continuously removed from the reaction mixture.
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The conjugate base of glyoxylic acid is known as glyoxylate and is the form that the compound exists in solution at neutral pH. Glyoxylate is the byproduct of the amidation process in biosynthesis of several amidated peptides. For the historical record, glyoxylic acid was prepared from oxalic acid electrosynthetically: in organic synthesis, lead dioxide cathodes were applied for preparing glyoxylic acid from oxalic acid in a sulfuric acid electrolyte. :380px Hot nitric acid can oxidize glyoxal to glyoxylic; however this reaction is highly exothermic and prone to thermal runaway.
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Aluminium chloride is manufactured on a large scale by the exothermic reaction of aluminium metal with chlorine or hydrogen chloride at temperatures between . :2 Al + 3 Cl2 → 2 AlCl3 :2 Al + 6 HCl → 2 AlCl3 \+ 3 H2 Aluminum chloride may be formed via a single displacement reaction between copper chloride and aluminum metal. :2 Al + 3 CuCl2 → 2 AlCl3 \+ 3 Cu In the US in 1993, approximately 21,000 tons were produced, not counting the amounts consumed in the production of aluminium. Hydrated aluminium trichloride is prepared by dissolving aluminium oxides in hydrochloric acid.
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He built this into the largest manufacturer of exothermic chemicals for foundries and steel mills in the U.S. and subsequently merged the company with its British licensor. Following this, he became Chairman of the North America division. In 1968 he resigned his position in Foseco and founded Morgenthaler Associates and subsequently, Morgenthaler Ventures, one of the few venture capitalists to do so using his own capital. Over the next 42 years, Morgenthaler Ventures invested in more than 300 companies in information technology and life sciences and bought industrial companies as a private equity firm.
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The cation was first reported in 1923 with a nitrate anion as a byproduct of the reduction of silver nitrate with a suspension of copper powder in acetonitrile. [Cu(CH3CN)4]PF6 is generally produced by the addition of HPF6 to a suspension of copper(I) oxide in acetonitrile: :Cu2O + 2 HPF6 \+ 8 CH3CN → 2 [Cu(CH3CN)4]PF6 \+ H2O The reaction is highly exothermic, and may bring the solution to a boil. Upon crystallization, the resulting microcrystals should be white, though a blue tinge is common, indicating the presence of Cu2+ impurities.
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Bags of cement routinely have health and safety warnings printed on them, because not only is cement highly alkaline, but the setting process is also exothermic. As a result, wet cement is strongly caustic, and can easily cause severe skin burns if not promptly washed off with water. Similarly, dry cement powder in contact with mucous membranes can cause severe eye or respiratory irritation. The reaction of cement dust with moisture in the sinuses and lungs can also cause a chemical burn, as well as headaches, fatigue, and lung cancer.
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The catalyst structure affects the proportion of the NH3 that is dissociated in reaction 3; a higher temperature is desirable for rocket thrusters, while more molecules are desirable when the reactions are intended to produce greater quantities of gas. Other variants of hydrazine that are used as rocket fuel are monomethylhydrazine, (CH3)NH(NH2) (also known as MMH), and unsymmetrical dimethylhydrazine, (CH3)2N(NH2) (also known as UDMH). These derivatives are used in two-component rocket fuels, often together with dinitrogen tetroxide, N2O4. These reactions are extremely exothermic, and the burning is also hypergolic (it starts burning without any external ignition).
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Principle of a LD converter Cross-section of a basic oxygen furnace The outside of a basic oxygen steelmaking plant at the Scunthorpe steel works. Basic oxygen steelmaking is a primary steelmaking process for converting molten pig iron into steel by blowing oxygen through a lance over the molten pig iron inside the converter. Exothermic heat is generated by the oxidation reactions during blowing. The basic oxygen steel-making process is as follows: # Molten pig iron (sometimes referred to as "hot metal") from a blast furnace is poured into a large refractory-lined container called a ladle.
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Diagram and cross section of an AN M18 smoke grenade A typical design consists of a sheet steel cylinder with four emission holes on top and one on the bottom to allow smoke release when the grenade is ignited. The filler consists of 250 to 350 grams of colored smoke composition (mostly potassium chlorate, lactose, and a dye) in virtually any color. White smoke grenades typically use hexachloroethane-zinc and granular aluminum. The reaction is exothermic and though they remain intact, smoke grenade casings will often remain scalding hot for some time even after the grenade is no longer emitting smoke.
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It could therefore be theorised that similar technologies might also be used in the context of terraformation on Venus. It can also be noted that the chemical reaction that converts minerals and carbon dioxide into carbonates is exothermic, in essence producing more energy than is consumed by the reaction. This opens up the possibility of creating self-reinforcing conversion processes with potential for exponential growth of the conversion rate until most of the atmospheric carbon dioxide can be converted. Bombardment of Venus with refined magnesium and calcium from off-world could also sequester carbon dioxide in the form of calcium and magnesium carbonates.
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For example, with Wilkinson's catalyst, one triphenylphosphine ligand must dissociate to give the coordinatively unsaturated 14-electron species which can participate in the catalytic cycle: :Wilkinson's catalyst requires activation before it can participate in the catalytic cycle Similarly, for an autocatalytic reaction, where one of the reaction products catalyzes the reaction itself, the rate of reaction is low initially until sufficient products have formed to catalyze the reaction. Reactions generally accelerate when heat is applied. Where a reaction is exothermic, the rate of the reaction may initially be low. As the reaction proceeds, heat is generated, and the rate of reaction increases.
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This procedure is known as Computer-Aided Cooling Curve Thermal Analysis. Advanced techniques use differential curves to locate endothermic inflection points such as gas holes, and shrinkage, or exothermic phases such as carbides, beta crystals, inter crystalline copper, magnesium silicide, iron phosphide's and other phases as they solidify. Detection limits seem to be around 0.01% to 0.03% of volume. In addition, integration of the area between the zero curve and the first derivative is a measure of the specific heat of that part of the solidification which can lead to rough estimates of the percent volume of a phase.
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If catabolism of alcohol goes all the way to completion, then, we have a very exothermic event yielding some of energy. If the reaction stops part way through the metabolic pathways, which happens because acetic acid is excreted in the urine after drinking, then not nearly as much energy can be derived from alcohol, indeed, only . At the very least, the theoretical limits on energy yield are determined to be to . It is also important to note that step 1 on this reaction is endothermic, requiring of alcohol, or about 3 molecules of adenosine triphosphate (ATP) per molecule of ethanol.
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RFNA increases the flammability of combustible materials and is highly exothermic when reacting with water. It is usually used with an inhibitor (with various, sometimes secret, substances, including hydrogen fluoride; any such combination is called inhibited RFNA, IRFNA) because nitric acid attacks most container materials. Hydrogen fluoride for instance will passivate the container metal with a thin layer of metal fluoride, making it nearly impervious to the nitric acid. It can also be a component of a monopropellant; with substances like amine nitrates dissolved in it, it can be used as the sole fuel in a rocket.
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The quantity of heat absorbed or given off during transformation is called the heat of formation. Heats of formations for solids and gases found in explosive reactions have been determined for a temperature of 25 °C and atmospheric pressure, and are normally given in units of kilojoules per gram-molecule. A positive value indicates that heat is absorbed during the formation of the compound from its elements; such a reaction is called an endothermic reaction. In explosive technology only materials that are exothermic—that have a net liberation of heat and have a negative heat of formation—are of interest.
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The flames caused as a result of a fuel undergoing combustion (burning) Air pollution abatement equipment provides combustion control for industrial processes. Combustion, or burning,colloquial meaning of burning is combustion accompanied by flames is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion does not always result in fire, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion (e.g.
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The solubility of calcium hydroxide at 70 °C is about half of its value at 25 °C. The reason for this rather uncommon phenomenon is that the dissolution of calcium hydroxide in water is an exothermic process, and also adheres to Le Chatelier's principle. A lowering of temperature thus favours the elimination of the heat liberated through the process of dissolution and increases the equilibrium constant of dissolution of Ca(OH)2, and so increase its solubility at low temperature. This counter- intuitive temperature dependence of the solubility is referred to as "retrograde" or "inverse" solubility.
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UHTCs possess simple empirical formulas and thus can be prepared by a wide variety of synthetic methods. UHTCs such as ZrB2 can be synthesized by stoichiometric reaction between constituent elements, in this case Zr and B. This reaction provides for precise stoichiometric control of the materials. At 2000 K, the formation of ZrB2 via stoichiometric reaction is thermodynamically favorable (ΔG=−279.6 kJ mol−1) and therefore, this route can be used to produce ZrB2 by self-propagating high-temperature synthesis (SHS). This technique takes advantage of the high exothermic energy of the reaction to cause high temperature, fast combustion reactions.
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' These additives often include wetting agents such as alkyl aryl sulfonates, but the exact nature of these additives are not known for commercial drain cleaners, as they are regarded as the trade secrets that make each drain cleaner unique to its brand. The aluminum granules that are included in the solid caustic drain cleaner is an aluminum oxide that breaks down and re-oxidizes to release hydrogen gas. The components of this reaction are shown below. Because the release of hydrogen gas is overall an exothermic reaction, the extra heat released helps to break down the greases, oils, etc.
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Reactions including the use of sodium hydride in DMF as a solvent are somewhat hazardous; exothermic decompositions have been reported at temperatures as low as 26 °C. On a laboratory scale any thermal runaway is (usually) quickly noticed and brought under control with an ice bath and this remains a popular combination of reagents. On a pilot plant scale, on the other hand, several accidents have been reported.UK Chemical Reaction Hazards Forum and references cited therein On the 20 of June 2018, the Danish Environmental Protective Agency published an article about the DMF's use in squishies.
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Another potential solid-state refrigeration technique and a relatively new area of study comes from a special property of super elastic materials. These materials undergo a temperature change when experiencing an applied mechanical stress (called the elastocaloric effect). Since super elastic materials deform reversibly at high strains, the material experiences a flattened elastic region in its stress-strain curve caused by a resulting phase transformation from an austenitic to a martensitic crystal phase. When a super elastic material experiences a stress in the austenitic phase, it undergoes an exothermic phase transformation to the martensitic phase, which causes the material to heat up.
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Simple Benson model of isobutylbenzene As stated above, BGIT can be used to calculate heats of formation, which are important in understanding the strengths of bonds and entire molecules. Furthermore, the method can be used to quickly estimate whether a reaction is endothermic or exothermic. These values are for gas-phase thermodynamics and typically at 298 K. Benson and coworkers have continued collecting data since their 1958 publication and have since published even more group increments, including strained rings, radicals, halogens, and more.S. W. Benson, Thermochemical Kinetics: Methods for the Estimation of Thermochemical Data and Rate Parameters 2d ed.
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One common laboratory instrument is the reaction calorimeter, where the heat flow from or into the reaction vessel is monitored. The heat release and corresponding energy change, Δ, of a combustion reaction can be measured particularly accurately. The measured heat energy released in an exothermic reaction is converted to ΔH⚬ in Joule per mole (formerly cal/mol). The standard enthalpy change ΔH⚬ is essentially the enthalpy change when the stoichiometric coefficients in the reaction are considered as the amounts of reactants and products (in mole); usually, the initial and final temperature is assumed to be 25 °C.
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Plasma recombination is a process by which positive ions of a plasma capture a free (energetic) electron and combine with electrons or negative ions to form new neutral atoms (gas). Recombination is an exothermic reaction, meaning heat releasing reaction. Recombination usually takes place in the whole volume of a plasma (volume recombination), although in some cases it is confined to some special region of it. Each kind of reaction is called a recombining mode and their individual rates are strongly affected by the properties of the plasma such as its energy (heat), density of each species, pressure and temperature of the surrounding environment.
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Thermal runaway is also called thermal explosion in chemical engineering, or runaway reaction in organic chemistry. It is a process by which an exothermic reaction goes out of control: the reaction rate increases due to an increase in temperature, causing a further increase in temperature and hence a further rapid increase in the reaction rate. This has contributed to industrial chemical accidents, most notably the 1947 Texas City disaster from overheated ammonium nitrate in a ship's hold, and the 1976 explosion of zoalene, in a drier, at King's Lynn. Frank- Kamenetskii theory provides a simplified analytical model for thermal explosion.
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BF3 is commonly referred to as "electron deficient," a description that is reinforced by its exothermic reactivity toward Lewis bases. In the boron trihalides, BX3, the length of the B–X bonds (1.30 Å) is shorter than would be expected for single bonds, and this shortness may indicate stronger B–X π-bonding in the fluoride. A facile explanation invokes the symmetry-allowed overlap of a p orbital on the boron atom with the in-phase combination of the three similarly oriented p orbitals on fluorine atoms. Others point to the ionic nature of the bonds in BF3.
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Video of a barking dog reaction by Maxim Bilovitskiy The "Barking Dog" is an exothermic chemical reaction that results from the ignition of a mixture of carbon disulfide and nitrous oxide. When ignited in a cylindrical tube, the reaction produces a bright flash and a loud "woof" - reminiscent of a barking dog. In simple terms, the ‘Barking Dog’ reaction is a combustion process, in which a fuel (carbon disulfide, CS2) reacts with an oxidizing agent (nitrous oxide, N2O), producing heat and elemental sulfur. The flame front in the reaction is a zone of very hot, luminous gas, produced by the reactants decomposing.
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We add the reaction sequence together. :C(graphite, s) \+ ½O2(g) \+ ½O2(g) → CO2(g) or :C(graphite, s) \+ O2(g) → CO2(g), Reaction (1) To figure out ΔH, we add the ΔH of the two equations in the reaction sequence: :(−110.5 kJ) + (−283.0 kJ) = (−393.5 kJ) = ΔH of Reaction (1) EXAMPLE OF THERMOCHEMICAL EQUATION IS When methane gas is combusted, heat is released, making the reaction exothermic. ... In the process, 890.4 kJ is released and so it is written as a product of the reaction. A thermochemical equation is a chemical equation that includes the enthalpy change of the reaction.
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The addition of hydrogen to double or triple bonds in hydrocarbons is a type of redox reaction that can be thermodynamically favorable. For example, the addition of hydrogen to ethene has a Gibbs free energy change of -101 kJ·mol−1, which is highly exothermic. In the hydrogenation of vegetable oils and fatty acids, for example, the heat released, about 25 kcal per mole (105 kJ/mol), is sufficient to raise the temperature of the oil by 1.6–1.7 °C per iodine number drop. However, the reaction rate for most hydrogenation reactions is negligible in the absence of catalysts.
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Zeman and Lackner outlined a specific method of air capture. First, CO2 is absorbed by an alkaline NaOH solution to produce dissolved sodium carbonate. The absorption reaction is a gas liquid reaction, strongly exothermic, here: :2NaOH(aq) + CO2(g) → Na2CO3(aq) + H2O(l) :Na2CO3(aq) + Ca(OH)2(s) → 2NaOH(aq) + CaCO3(s) :ΔH° = -114.7 kJ/mol Causticization is performed ubiquitously in the pulp and paper industry and readily transfers 94% of the carbonate ions from the sodium to the calcium cation. Subsequently, the calcium carbonate precipitate is filtered from solution and thermally decomposed to produce gaseous CO2.
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The industrial production of ammonium nitrate entails the acid-base reaction of ammonia with nitric acid: :HNO3 \+ NH3 → NH4NO3 Ammonia is used in its anhydrous form (a gas) and the nitric acid is concentrated. The reaction is violent owing to its highly exothermic nature. After the solution is formed, typically at about 83% concentration, the excess water is evaporated off to leave an ammonium nitrate (AN) content of 95% to 99.9% concentration (AN melt), depending on grade. The AN melt is then made into "prills" or small beads in a spray tower, or into granules by spraying and tumbling in a rotating drum.
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In a conventional chemical rocket engine, the rocket carries both its fuel and oxidizer in its fuselage. The chemical reaction between the fuel and the oxidizer produces reactant products which are nominally gasses at the pressures and temperatures in the rocket's combustion chamber. The reaction is also highly energetic (exothermic) releasing tremendous energy in the form of heat; that is imparted to the reactant products in the combustion chamber giving this mass enormous internal energy which, when expanded through a nozzle is capable of producing very high exhaust velocities. The exhaust is directed rearward through the nozzle, thereby producing a thrust forward.
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A demonstration of the reaction of the exothermic reaction of the strong Lewis acid (Al2Br6) and strong Lewis base (H2O). Al2Br6 dissociates readily to give the strong Lewis acid, AlBr3. Regarding the tendency of Al2Br6 to dimerize, it is common for heavier main group halides to exist as aggregates larger than implied by their empirical formulae. Lighter main group halides such as boron tribromide do not show this tendency, in part due to the smaller size of the central atom. Consistent with its Lewis acidic character, water hydrolizes Al2Br6 with evolution of HBr and formation of Al-OH-Br species.
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Sodium hydroxide reacts with protic acids to produce water and the corresponding salts. For example, when sodium hydroxide reacts with hydrochloric acid, sodium chloride is formed: :NaOH(aq) + HCl(aq) -> NaCl(aq) +H2O(l) In general, such neutralization reactions are represented by one simple net ionic equation: :OH- (aq) + H+(aq) -> H2O (l) This type of reaction with a strong acid releases heat, and hence is exothermic. Such acid-base reactions can also be used for titrations. However, sodium hydroxide is not used as a primary standard because it is hygroscopic and absorbs carbon dioxide from air.
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Sulfur dioxide is introduced with steam and nitrogen dioxide into large chambers lined with sheet lead where the gases are sprayed down with water and chamber acid (62–70% sulfuric acid). The sulfur dioxide and nitrogen dioxide dissolve, and over a period of approximately 30 minutes the sulfur dioxide is oxidized to sulfuric acid. The presence of nitrogen dioxide is necessary for the reaction to proceed at a reasonable rate. The process is highly exothermic, and a major consideration of the design of the chambers was to provide a way to dissipate the heat formed in the reactions.
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Other boranes are electrophilic and react vigorously with reagents that can supply electron pairs. With an alkali metal hydride, for example, :B2H6 \+ 2 H− → 2 BH4− Further demonstrating that they are not in general "electron-deficient" (see above), boranes can also function as electron donors owing to the relative basic character of the low-polarity B-Hterminal groups, as in reactions with halogens to form haloboranes. The reaction of some lower boranes with air is strongly exothermic; those of B2H6 and B5H9, for example, occur explosively except in very low concentration. This does not result from any inherent instability in the boranes.
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This pressurized gas applies pressure to the sample from all directions while the oven is heated. The heat and pressure cause the graphite and metallic chromium to react and form chromium carbide. Decreasing the percentage of carbon content in the initial mixture results in an increase in the yield of the Cr7C3, and Cr23C6 forms of chromium carbide. Another method for the synthesis of chromium carbide utilizes chromium oxide, pure aluminum, and graphite in a self-propagating exothermic reaction that proceeds as follows: :3Cr2O3 \+ 6Al + 4C → 2Cr3C2 \+ 3Al2O3 In this method the reactants are ground and blended in a ball mill.
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The catalyst protonates the alkenes (propene, butene) to produce reactive carbocations, which alkylate isobutane. The reaction is carried out at mild temperatures (0-30 °C) in a two-phase reaction. Because the reaction is exothermic, cooling is needed: SAAU plants require lower temperatures so the cooling medium needs to be chilled, for HFAU normal refinery cooling water will suffice. It is important to keep a high ratio of Isobutane to Alkene at the point of reaction to prevent side reactions which produces a lower octane product, so the plants have a high recycle of Isobutane back to feed.
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156–62 The surface-supplied divers evaluated the use of heliox due to the depth of the wreck. It also proved to be successful once the dive tables were adjusted.Southerland; Davidson; Journal, 2001 A Navy diver prepares "the spider" The turret, moments after it reached the surface, secure in the "spider" lifting frame Much like the previous year, the 2002 dive season was dedicated to lifting the turret to the surface. Around 160 divers were assigned to remove the parts of the hull, including the armor belt, that lay on top of the turret using chisels, exothermic cutting torches and hydroblasters.
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Cladding for nuclear reactor fuels consumes about 1% of the zirconium supply, mainly in the form of zircaloys. The desired properties of these alloys are a low neutron-capture cross-section and resistance to corrosion under normal service conditions. Efficient methods for removing the hafnium impurities were developed to serve this purpose. One disadvantage of zirconium alloys is that zirconium reacts with water at high temperatures, producing hydrogen gas and accelerated degradation of the fuel rod cladding: : Zr + 2 H2O → ZrO2 \+ 2 H2 This exothermic reaction is very slow below 100 °C, but at temperature above 900 °C the reaction is rapid.
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The rapid heating can lead to significantly lower resin viscosities, and this in turn allows achieving full laminate consolidation using pressures lower than those used in autoclave. The mold and laminate become separated from the circulating HTF by a flexible membrane. The part, typically under full vacuum, is subject to pressures as high as 250kPa fluid pressure and can be rapidly heated to the desired cure temperature without risk of catastrophic exothermic reaction, as the HTF can draw excess heat as desired. The air is then removed under vacuum and the laminate is compacted and heated until the part is cured.
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This sequence of reactions can be understood by thinking of the two interacting carbon nuclei as coming together to form an excited state of the 24Mg nucleus, which then decays in one of the five ways listed above. The first two reactions are strongly exothermic, as indicated by the large positive energies released, and are the most frequent results of the interaction. The third reaction is strongly endothermic, as indicated by the large negative energy indicating that energy is absorbed rather than emitted. This makes it much less likely, yet still possible in the high-energy environment of carbon burning.
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A sodium acetate heat pad Disposable chemical pads employ a one-time exothermic chemical reaction. One type, frequently used for hand warmers, is triggered by unwrapping an air-tight packet containing slightly moist iron powder and salt or catalysts which rusts over a period of hours after being exposed to oxygen in the air. Another type contains separate compartments within the pad; when the user squeezes the pad, a barrier ruptures and the compartments mix, producing heat such as the enthalpy change of solution of calcium chloride dissolving. The most common reusable heat pads contain a supersaturated solution of sodium acetate in water.
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When a protostar is formed from the collapse of a giant molecular cloud of gas and dust in the local interstellar medium, the initial composition is homogeneous throughout, consisting of about 70% hydrogen, 28% helium and trace amounts of other elements, by mass. The initial mass of the star depends on the local conditions within the cloud. (The mass distribution of newly formed stars is described empirically by the initial mass function.) During the initial collapse, this pre-main-sequence star generates energy through gravitational contraction. Once sufficiently dense, stars begin converting hydrogen into helium and giving off energy through an exothermic nuclear fusion process.
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A pair of flameless ration heaters A flameless ration heater (FRH) is a form of self-heating food packaging included with meals, ready-to-eat (MREs), used to heat the food. United States military specifications for the heater require it be capable of raising the temperature of an entrée (American English for main course) by in twelve minutes, and that it has no visible flame. The ration heater contains finely powdered magnesium metal, alloyed with a small amount of iron, and table salt. To activate the reaction, a small amount of water is added, and the boiling point of water is quickly reached as the exothermic reaction proceeds.
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Gas-phase microreactors have a long history but those involving liquids started to appear in the late 1990s. One of the first microreactors with embedded high performance heat exchangers were made in the early 1990s by the Central Experimentation Department (Hauptabteilung Versuchstechnik, HVT) of Forschungszentrum Karlsruhe in Germany, using mechanical micromachining techniques that were a spinoff from the manufacture of separation nozzles for uranium enrichment. As research on nuclear technology was drastically reduced in Germany, microstructured heat exchangers were investigated for their application in handling highly exothermic and dangerous chemical reactions. This new concept, known by names as microreaction technology or micro process engineering, was further developed by various research institutions.
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It is postulated that the breakpoint is revealed by the difference in reaction enthalpies between the formation of the Cu-EDTA complex, and that for the formation of the Cu-amine complex. Fig. 16. Thermometric EDTA titration determination of trace Cu(II) by Mn(II) catalysis of exothermic reaction between hydrogen peroxide and polyhydric phenol. A catalyzed endpoint procedure to determine trace amounts of metal ions in solution (down to approximately 10 mg/L) employs 0.01 mol/L EDTA. This has been applied to the determination of low level Cu(II) in specialized plating baths, and to the determination of total hardness in water.
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The resulting sodium sulfate from these processes is known as salt cake. :Mannheim: 2 NaCl + H2SO4 → 2 HCl + Na2SO4 :Hargreaves: 4 NaCl + 2 SO2 \+ O2 \+ 2 H2O → 4 HCl + 2 Na2SO4 The second major production of sodium sulfate are the processes where surplus sodium hydroxide is neutralised by sulfuric acid, as applied on a large scale in the production of rayon. This method is also a regularly applied and convenient laboratory preparation. : 2 NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2 H2O(l) ΔH = -112.5 kJ (highly exothermic) In the laboratory it can also be synthesized from the reaction between sodium bicarbonate and magnesium sulfate.
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When used for cutting, the plasma gas flow is increased so that the deeply penetrating plasma jet cuts through the material and molten material is removed as cutting dross. PAC differs from oxy-fuel cutting in that the plasma process operates by using the arc to melt the metal whereas in the oxy-fuel process, the oxygen oxidizes the metal and the heat from the exothermic reaction melts the metal. Unlike oxy-fuel cutting, the PAC process can be applied to cutting metals which form refractory oxides such as stainless steel, cast iron, aluminum and other non-ferrous alloys. Since PAC was introduced by Praxair Inc.
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Other N-H compounds, such as amides and ureas, react much more slowly with MIC. It also reacts with itself to form a trimer or higher molecular weight polymers. In the presence of catalysts, MIC reacts with itself to form a solid trimer, trimethyl isocyanurate, or a higher molecular weight polymer: none Sodium methoxide, triethyl phosphine, ferric chloride and certain other metal compounds catalyze the formation of the MIC- trimer, while the high-molecular-weight polymer formation is catalyzed by certain trialkylamines. Since the formation of the MIC trimer is exothermic (298 calories per gram of MIC), the reaction can lead to violent boiling of the MIC.
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In the ecosystems, hydrogen can be produced through biological and abiotic processes . The abiotic processes are mainly due to geothermal production and serpentinization. In the first case, hydrogen is usually present as a gas and probably can be obtained by different reactions: 1\. Water may react with silicon radical at high temperature: Si· + H2O → SiOH + H· H· + H· → H2 2\. The proposed reaction between iron oxides and water, at temperatures higher than 800°C: 2FeO + H2O → Fe2O3 \+ H2 2Fe3O4 \+ H2O → 3Fe2O3 \+ H2 On the other hand, serpentinization is an exothermic geochemical mechanism that occurs when, thanks to the tectonic movements, the ultramafic rocks raise and reach the water.
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The limestone blocks were then crushed, afterwards slaked (the process of adding water and constantly turning the lime to create a chemical reaction, whereby the burnt lime, or what is known also as calcium oxide,Slaking is a strongly exothermic reaction in which quicklime absorbs hydrogen and oxygen from water to produce lime — a fine- grained white powder (Eliyahu-Behar, A., et al. 2017). is changed into calcium hydroxide), and mixed with an aggregate to form an adhesive paste used in construction and for daubing buildings. When properly burnt, limestone loses its carbonic acid () and becomes converted into caustic or quicklime (CaO).Young, Clyde; Engel, Bernard (1943), p.
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The exothermic heat generated by the polymerization processes is dissipated constantly while the temperature may rise rapidly to over 75 °C in the first minutes, after which it falls slowly. After 69 hr the gel has reached room temperature, and thus, is in its lowest energy state because the chemical reactions and the gelation are terminated. Gelation means that the solvent (water) gets immobilized within the polymer network by means of hydrogen bonds and also van der Waals forces. As a result, the prepared gel is homogeneous (in terms of homogeneous distribution of cross-links throughout the gel sample), inherently stable and free of monomers or radicals.
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Also known by the Unified Intelligence-Taskforce (UNIT) as Stingrays, they are flying manta ray-like creatures, with metal exoskeletons that allow them to travel from planet to planet via wormholes. They consume everything on a planet, turning it into desert; and then swarm over the planet's surface, generating a wormhole which allows them to travel to the next planet. The Stingrays are apparently arthropods, as they are exothermic, and possess an exoskeleton composed of metal that has been ingested then exuded to the exoskeleton. They are voracious feeders, eating both organic and inorganic materials ranging from flesh and bone to plant matter to metals and plastic.
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The company also produced several utility based vehicles based on their snowcat tracked vehicle, in addition to larger snow grooming machines suitable for use on steep ski-slopes. Thiokol machines were used in ski resorts, operated by the USAF in Alaska and other northern regions, and are now popular with private owners as dependable snowcats and for all-terrain transport. Amphibious Thiokol Swamp Spryte All Terrain Vehicle Thiokol pioneered the short-burn rocket motors used in aircraft ejection seats. The company also produced a number of the earliest practical airbag systems, building the high-speed sodium azide exothermic gas generators used to inflate the bags.
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The spitting spiders Scytodes can spit a venomous and sticky fluid that traps its victims and also poisons them. The bombardier beetle is unusual by using a violent exothermic chemical reaction to launch a boiling noxious chemical spray in a rapid burst of pulses from special glands in its abdomen, accompanied with a popping sound. The Anthia (oogpister beetle) will fire formic acid at attackers, probably extracting the formic acid from the ants that it eats. The devil-rider stick insects (Anisomorpha) can fire terpenes from glands on the metathorax that can cause an intense burning irritation of the eyes and mouth of potential predators.
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In the 1980s, the use of cadaver allograft disc for filling in small holes received a satisfactory result, and there was a resurgence of the use of cadaver bone. However, cadaver bones and allografts, in general, are not the preferred materials in modern operations. The use of methyl methacrylate (PMMA) for cranioplasty was being developed since World War II, and the material is used extensively since 1954, when there is a high demand for cranioplasty due to a large number of injuries. It becomes malleable when an exothermic reaction occurs between its powder form and benzoyl peroxide, allowing it to be moulded to the cranial defect.
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The rate coefficients and products of many high-temperature gas-phase reactions change if an inert gas is added to the mixture; variations on this effect are called fall-off and chemical activation. These phenomena are due to exothermic or endothermic reactions occurring faster than heat transfer, causing the reacting molecules to have non-thermal energy distributions (non- Boltzmann distribution). Increasing the pressure increases the heat transfer rate between the reacting molecules and the rest of the system, reducing this effect. Condensed-phase rate coefficients can also be affected by pressure, although rather high pressures are required for a measurable effect because ions and molecules are not very compressible.
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In general terms, the free energy change (ΔG) of a reaction determines whether a chemical change will take place, but kinetics describes how fast the reaction is. A reaction can be very exothermic and have a very positive entropy change but will not happen in practice if the reaction is too slow. If a reactant can produce two products, the thermodynamically most stable one will form in general, except in special circumstances when the reaction is said to be under kinetic reaction control. The Curtin-Hammett principle applies when determining the product ratio for two reactants interconverting rapidly, each going to a distinct product.
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If ΔS and/or T are small, the condition ΔG < 0 may imply that ΔH < 0, which would indicate an exothermic reaction. However, this is not required; endothermic reactions can proceed spontaneously if the TΔS term is large enough. Moreover, the slopes of the derivatives of ΔG and ΔH converge and are equal to zero at T = 0\. This ensures that ΔG and ΔH are nearly the same over a considerable range of temperatures and justifies the approximate empirical Principle of Thomsen and Berthelot, which states that the equilibrium state to which a system proceeds is the one that evolves the greatest amount of heat, i.e.
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As of 2006, only a few smaller plants continue to use benzene. In both cases, benzene and butane are fed into a stream of hot air, and the mixture is passed through a catalyst bed at high temperature. The ratio of air to hydrocarbon is controlled to prevent the mixture from igniting. Vanadium pentoxide and molybdenum trioxide are the catalysts used for the benzene route, whereas vanadium phosphate is used for the butane route: :C4H10 \+ 3.5 O2 → C4H2O3 \+ 4 H2O ∆H = −1236 kJ/mol The main competing process entails full combustion of the butane, a conversion that is twice as exothermic as the partial oxidation.
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For example, oxidation of cyclohexane into cyclohexanol and cyclohexanone and ortho-xylene into phthalic anhydride have led to catastrophic explosions when reaction control failed. Thermal runaway may result from unwanted exothermic side reaction(s) that begin at higher temperatures, following an initial accidental overheating of the reaction mixture. This scenario was behind the Seveso disaster, where thermal runaway heated a reaction to temperatures such that in addition to the intended 2,4,5-trichlorophenol, poisonous 2,3,7,8-tetrachlorodibenzo-p-dioxin was also produced, and was vented into the environment after the reactor's rupture disk burst. Thermal runaway is most often caused by failure of the reactor vessel's cooling system.
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ValuJet workers then loaded the boxes in the cargo hold in the mistaken belief that the devices that they contained were just empty canisters, thus being certified as supposedly "safe" to transport on a passenger aircraft, when in fact they were neither simple oxygen canisters, nor empty.Mayday, "Fire in the Hold", season 12 episode 2 Chemical oxygen generators, when activated, produce oxygen for passengers if the plane suffers a decompression. However, they also produce a great quantity of heat due to the exothermic nature of the chemical reaction involved. Therefore, not only could the heat and generated oxygen start a fire, but the oxygen could also keep the fire burning.
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The basic principle underlying this technique is that when the sample undergoes a physical transformation such as phase transitions, more or less heat will need to flow to it than the reference to maintain both at the same temperature. Whether less or more heat must flow to the sample depends on whether the process is exothermic or endothermic. For example, as a solid sample melts to a liquid, it will require more heat flowing to the sample to increase its temperature at the same rate as the reference. This is due to the absorption of heat by the sample as it undergoes the endothermic phase transition from solid to liquid.
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While the formation enthalpy of is higher than that of , the formation entropy is much lower. Consequently, the standard free energy of formation of from its component elements is almost constant and independent of the temperature, while the free energy of formation of decreases with temperature.List of standard Gibbs free energies of formation At high temperatures, the forward reaction becomes endergonic, favoring the (exergonic) reverse reaction toward CO, even though the forward reaction is still exothermic. The effect of temperature on the extent of the Boudouard reaction is indicated better by the value of the equilibrium constant than by the standard free energy of reaction.
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Iodomethane is formed via the exothermic reaction that occurs when iodine is added to a mixture of methanol with red phosphorus. The iodinating reagent is phosphorus triiodide that is formed in situ: :3 CH3OH + PI3 → 3 CH3I + H2PO3H Alternatively, it is prepared from the reaction of dimethyl sulfate with potassium iodide in the presence of calcium carbonate: :(CH3O)2SO2 \+ KI -> CH3I + CH3OSO2OK Iodomethane can also be prepared by the reaction of methanol with aqueous hydrogen iodide: : CH3OH + HI -> CH3I + H2O The generated iodomethane can be distilled from the reaction mixture. Iodomethane may also be prepared by treating iodoform with potassium hydroxide and dimethyl sulfate under 95% ethanol.
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The MRE has been in continuous development since its introduction. In 1990, a Flameless Ration Heater (FRH), a water-activated exothermic reaction product that emits heat, allowed a service member in the field to enjoy a hot meal. In an array of field tests and surveys, service members requested more entrée options and larger serving sizes. By 1994, commercial-like graphics (images) were added to make the packets more user-friendly and appealing, while biodegradable materials were introduced for inedible components, such as spoons and napkins. The number of main dishes expanded to 16 by 1996 (including vegetarian options), 20 by 1997 and 24 by 1998.
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Space-filling model representation of dioxygen (O2) molecule The common allotrope of elemental oxygen on Earth is called dioxygen, , the major part of the Earth's atmospheric oxygen (see Occurrence). O2 has a bond length of 121 pm and a bond energy of 498 kJ/mol, which is smaller than the energy of other double bonds or pairs of single bonds in the biosphere and responsible for the exothermic reaction of O2 with any organic molecule. Due to its energy content, O2 is used by complex forms of life, such as animals, in cellular respiration. Other aspects of are covered in the remainder of this article.
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There is an industrial coatings process, known as evaporative deposition, whereby a solid material is heated to the gaseous state in a low-pressure chamber, the gas molecules travel across the chamber space and then deposit to the solid state on a target surface, forming a smooth and thin layer on the target surface. Again, the molecules do not go through an intermediate liquid state when going from the gas to the solid. See also physical vapor deposition, which is a class of processes used to deposit thin films of various materials onto various surfaces. Deposition releases energy and is an exothermic phase change.
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In combination with entropy determinations, it is also used to predict whether a reaction is spontaneous or non-spontaneous, favorable or unfavorable. Endothermic reactions absorb heat, while exothermic reactions release heat. Thermochemistry coalesces the concepts of thermodynamics with the concept of energy in the form of chemical bonds. The subject commonly includes calculations of such quantities as heat capacity, heat of combustion, heat of formation, enthalpy, entropy, free energy, and calories. The world's first ice-calorimeter, used in the winter of 1782–83, by Antoine Lavoisier and Pierre-Simon Laplace, to determine the heat evolved in various chemical changes; calculations which were based on Joseph Black’s prior discovery of latent heat.
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SOFCs can also be fueled by externally reforming heavier hydrocarbons, such as gasoline, diesel, jet fuel (JP-8) or biofuels. Such reformates are mixtures of hydrogen, carbon monoxide, carbon dioxide, steam and methane, formed by reacting the hydrocarbon fuels with air or steam in a device upstream of the SOFC anode. SOFC power systems can increase efficiency by using the heat given off by the exothermic electrochemical oxidation within the fuel cell for endothermic steam reforming process. Additionally, solid fuels such as coal and biomass may be gasified to form syngas which is suitable for fueling SOFCs in integrated gasification fuel cell power cycles.
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When mixed with water, an exothermic reaction occurs and forms a hard white filling similar to density of fired ceramics. Different grades of plasters are available and vary based on their particle size, setting time, density, expansion, and color. A thermoplastic synthetic wax resin mixture developed by John W Burke and Steve Colton in 1997 can be used to compensate losses in objects from translucent materials such as alabaster, marble, calcite, diorite, and anhydrite. The mixture consists of polyvinyl acetate (PVAC) AYAC, ethylene acrylic acid (EAA) copolymers A-C 540, and 580, antioxidants Irganox 1076 or 1035, dry pigments, marble powder, and other additives which were all melted together.
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Because they are strongly oxidative, many oxygen–xenon compounds are toxic; they are also explosive (highly exothermic), breaking down to elemental xenon and diatomic oxygen (O2) with much stronger chemical bonds than the xenon compounds. Xenon gas can be safely kept in normal sealed glass or metal containers at standard temperature and pressure. However, it readily dissolves in most plastics and rubber, and will gradually escape from a container sealed with such materials. Xenon is non-toxic, although it does dissolve in blood and belongs to a select group of substances that penetrate the blood–brain barrier, causing mild to full surgical anesthesia when inhaled in high concentrations with oxygen.
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Ethanol was produced primarily by the sulfuric acid hydration process in which ethylene is reacted with sulfuric acid to produce ethyl sulfate followed by hydrolysis, but this method has been mostly replaced by direct hydration of ethylene. Ethyl sulfate can be produced in a laboratory setting by reacting ethanol with sulfuric acid under a gentle boil, while keeping the reaction below 140 °C. The sulfuric acid must be added dropwise or the reaction must be actively cooled because the reaction itself is highly exothermic. :CH3CH2OH + H2SO4 → CH3-CH2-O-SO3H + H2O If the temperature exceeds 140 °C, the ethyl sulfate product tends to react with residual ethanol starting material, producing diethyl ether.
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Effectively, the postulate states that the structure of a transition state resembles that of the species nearest to it in free energy. This can be explained with reference to potential energy diagrams: Energy diagrams showing how to interpret Hammond's Postulate In case (a), which is an exothermic reaction, the energy of the transition state is closer in energy to that of the reactant than that of the intermediate or the product. Therefore, from the postulate, the structure of the transition state also more closely resembles that of the reactant. In case (b), the energy of the transition state is close to neither the reactant nor the product, making none of them a good structural model for the transition state.
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Nuclear stability is limited to those combinations of protons and neutrons described by the chart of the nuclides, also called the valley of stability. The boundaries of this valley are the neutron drip line on the neutron rich side, and the proton drip line on the proton-rich side. These limits exist because of particle decay, whereby an exothermic nuclear transition can occur by the emission of one or more nucleons (not to be confused with particle decay in particle physics). As such, the drip line may be defined as the boundary beyond which proton or neutron separation energy becomes negative, favoring the emission of a particle from a newly formed unbound system.
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John Bernadou patented a single-base propellant while working at the Naval Torpedo Station in 1897. Bernadou's colloid of nitrocellulose with ether and alcohol was formulated for the reaction pressures generated within naval artillery. The colloid was extruded in dense cylinders with longitudinal perforations to decompose in accordance with Piobert's law. If all external surfaces of the grain are ignited simultaneously, the grain reacts inward from the outside of the cylinder (creating a reaction area of decreasing size), and outward from each perforation (creating a reaction area of increasing size.) Propellant decomposition is initiated by heat causing the colloid to melt and form bubbles of reactive gas which decompose in a luminous exothermic reaction after the bubbles burst.
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During the Industrial Revolution, demand for alkaline substances such as soda ash increased, and Nicolas Leblanc developed a new industrial-scale process for producing the soda ash. In the Leblanc process, salt was converted to soda ash, using sulfuric acid, limestone, and coal, giving hydrogen chloride as by-product. Initially, this gas was vented to air, but the Alkali Act of 1863 prohibited such release, so then soda ash producers absorbed the HCl waste gas in water, producing hydrochloric acid on an industrial scale. Later, the Hargreaves process was developed, which is similar to the Leblanc process except sulfur dioxide, water, and air are used instead of sulfuric acid in a reaction which is exothermic overall.
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Resonance (or delocalization) energy is the amount of energy needed to convert the true delocalized structure into that of the most stable contributing structure. The empirical resonance energy can be estimated by comparing the enthalpy change of hydrogenation of the real substance with that estimated for the contributing structure. The complete hydrogenation of benzene to cyclohexane via 1,3-cyclohexadiene and cyclohexene is exothermic; 1 mole of benzene delivers 208.4 kJ (49.8 kcal). 800px Hydrogenation of one mole of double bonds delivers 119.7 kJ (28.6 kcal), as can be deduced from the last step, the hydrogenation of cyclohexene. In benzene, however, 23.4 kJ (5.6 kcal) are needed to hydrogenate one mole of double bonds.
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Effectively, the postulate states that the structure of a transition state resembles that of the species nearest to it in free energy. This can be explained with reference to potential energy diagrams: right In case (a), which is an exothermic reaction, the energy of the transition state is closer in energy to that of the reactant than that of the intermediate or the product. Therefore, from the postulate, the structure of the transition state also more closely resembles that of the reactant. In case (b), the energy of the transition state is close to neither the reactant nor the product, making none of them a good structural model for the transition state.
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The ortho/para distinction also occurs in other hydrogen-containing molecules or functional groups, such as water and methylene, but is of little significance for their thermal properties. The ortho form that converts to the para form slowly at low temperatures. The ortho/para ratio in condensed H2 is an important consideration in the preparation and storage of liquid hydrogen: the conversion from ortho to para is exothermic and produces enough heat to evaporate some of the hydrogen liquid, leading to loss of liquefied material. Catalysts for the ortho-para interconversion, such as ferric oxide, activated carbon, platinized asbestos, rare earth metals, uranium compounds, chromic oxide, or some nickel compounds, are used during hydrogen cooling.
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Rocket propellant is mass that is stored, usually in some form of propellant tank, or within the combustion chamber itself, prior to being ejected from a rocket engine in the form of a fluid jet to produce thrust. Chemical rocket propellants are most commonly used, which undergo exothermic chemical reactions which produce hot gas which is used by a rocket for propulsive purposes. Alternatively, a chemically inert reaction mass can be heated using a high-energy power source via a heat exchanger, and then no combustion chamber is used. Solid rocket propellants are prepared as a mixture of fuel and oxidising components called 'grain' and the propellant storage casing effectively becomes the combustion chamber.
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An isodesmic reaction is a chemical reaction in which the type of chemical bonds broken in the reactant are the same as the type of bonds formed in the reaction product. This type of reaction is often used as a hypothetical reaction in thermochemistry. An example of an isodesmic reaction is :CH3− \+ CH3X -> CH4 \+ CH2X− (1) :X = F, Cl, Br, I Equation 1 describes the deprotonation of a methyl halide by a methyl anion. The energy change associated with this exothermic reaction which can be calculated in silico increases going from fluorine to chlorine to bromine and iodine making the CH2I− anion the most stable and least basic of all the halides.
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The unique advantages of microstructured reactors or microreactors are enhanced heat transfer due to the large surface area-to-volume ratio, and enhanced mass transfer. For example, the length scale of diffusion processes is comparable to that of microchannels or even shorter, and efficient mixing of reactants can be achieved during very short times (typically milliseconds). The good heat transfer properties allow a precise temperature control of reactions. For example, highly exothermic reactions can be conducted almost isothermally when the microstructured reactor contains a second set of microchannels ("cooling passage"), fluidically separated from the reaction channels ("reaction passage"), through which a flow of cold fluid with sufficiently high heat capacity is maintained.
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Depending on whether the reaction between the titrant and analyte is exothermic or endothermic, the temperature will either rise or fall during the titration. When all analyte has been consumed by reaction with the titrant, a change in the rate of temperature increase or decrease reveals the equivalence point and an inflection in the temperature curve can be observed. The equivalence point can be located precisely by employing the second derivative of the temperature curve. The software used in modern automated thermometric titration systems employ sophisticated digital smoothing algorithms so that "noise" resulting from the highly sensitive temperature probes does not interfere with the generation of a smooth, symmetrical second derivative "peak" which defines the endpoint.
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These types of models, as well as the observation that the degree two structure of the LLSVPs is orthogonal to the path of true polar wander, suggest these mantle structures have been stable over large amounts of time. This geometrical relationship is also consistent with the position of the supercontinent Pangaea, and the formation of the current geoid pattern due to continental break-up from the superswell below. However, the heat from the core is not enough to sustain the energy needed to fuel the superplume(s) located at the LLSVPs. There is a phase transition from perovskite to post-perovskite from the down welling slab(s) that causes an exothermic reaction.
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The fuel for the PEMFC is hydrogen, and the charge carrier is the hydrogen ion (proton). At the anode, the hydrogen molecule is split into hydrogen ions (protons) and electrons. The hydrogen ions permeate across the electrolyte to the cathode, while the electrons flow through an external circuit and produce electric power. Oxygen, usually in the form of air, is supplied to the cathode and combines with the electrons and the hydrogen ions to produce water. The reactions at the electrodes are as follows: :Anode reaction: ::2H2 → 4H+ \+ 4e− :Cathode reaction: ::O2 \+ 4H+ \+ 4e− → 2H2O :Overall cell reaction: ::2H2 \+ O2 → 2H2O + heat + electrical energy The theoretical exothermic potential is +1.23 V overall.
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The oxide layer produces heat primarily by decay heat, while the principal heat source in the metal layer is exothermic reaction with the water released from the concrete. Decomposition of concrete and volatilization of the alkali metal compounds consumes a substantial amount of heat. The fast erosion phase of the concrete basemat lasts for about an hour and progresses to about one meter in depth, then slows to several centimeters per hour, and stops completely when the melt cools below the decomposition temperature of concrete (about ). Complete melt-through can occur in several days even through several meters of concrete; the corium then penetrates several meters into the underlying soil, spreads around, cools and solidifies.
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When alkenes and alkynes are subjected to hydrogenation reaction by treating them with hydrogen in the presence of palladium or platinum or nickel catalyst, they produce alkanes. In this reaction powdered catalyst is preferred to increase the surface area so that adsorption of hydrogen on the catalyst increases. In this reaction the hydrogen gets attached on the catalyst to form a hydrogen-catalyst bond which leads to weakening of H-H bond, thereby leading to the addition of hydrogen on alkenes and alkynes. The reaction is exothermic because the product alkane is stable as it has more sigma bonds than the reactant alkenes and alkynes due to conversion of pi bond to sigma bonds.Harikiran.
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In electrical engineering, thermal runaway is typically associated with increased current flow and power dissipation, although exothermic chemical reactions can be of concern here too. Thermal runaway can occur in civil engineering, notably when the heat released by large amounts of curing concrete is not controlled. In astrophysics, runaway nuclear fusion reactions in stars can lead to nova and several types of supernova explosions, and also occur as a less dramatic event in the normal evolution of solar mass stars, the "helium flash". Some climate researchers have postulated that a global average temperature increase of 3–4 degrees Celsius above the preindustrial baseline could lead to a further unchecked increase in surface temperatures.
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During Polanyi's time at Princeton University, he worked with Sir Hugh Taylor and his colleagues, Michael Boudart and David Garvin. He was influenced by studies conducted at Princeton looking at the vibrationally excited reaction products between atomic hydrogen and ozone. When Polanyi moved to the University of Toronto, his first graduate students were looking for enhanced reaction rates with vibrationally excited hydrogen, as well as looking for the presence of vibrationally excited hydrogen chloride during the exothermic reaction of molecular chlorine with atomic hydrogen. Graduate student Kenneth Cashion was working with Polanyi when they made their first discoveries about chemiluminescence, the light emitted by an atom molecule when it is in an excited state.
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DSC makes a reasonable initial safety screening tool. In this mode the sample will be housed in a non-reactive crucible (often gold or gold- plated steel), and which will be able to withstand pressure (typically up to 100 bar). The presence of an exothermic event can then be used to assess the stability of a substance to heat. However, due to a combination of relatively poor sensitivity, slower than normal scan rates (typically 2–3 °C/min, due to much heavier crucible) and unknown activation energy, it is necessary to deduct about 75–100 °C from the initial start of the observed exotherm to suggest a maximal temperature for the material.
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Engines of similar (or even identical) configuration and operation may use a supply of heat from other sources such as nuclear, solar, geothermal or exothermic reactions not involving combustion; but are not then strictly classed as external combustion engines, but as external thermal engines. The working fluid can be a gas as in a Stirling engine, or steam as in a steam engine or an organic liquid such as n-pentane in an Organic Rankine cycle. The fluid can be of any composition; gas is by far the most common, although even single-phase liquid is sometimes used. In the case of the steam engine, the fluid changes phases between liquid and gas.
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Acetylene is not especially toxic, but when generated from calcium carbide, it can contain toxic impurities such as traces of phosphine and arsine, which give it a distinct garlic-like smell. It is also highly flammable, as are most light hydrocarbons, hence its use in welding. Its most singular hazard is associated with its intrinsic instability, especially when it is pressurized: under certain conditions acetylene can react in an exothermic addition-type reaction to form a number of products, typically benzene and/or vinylacetylene, possibly in addition to carbon and hydrogen. Consequently, acetylene, if initiated by intense heat or a shockwave, can decompose explosively if the absolute pressure of the gas exceeds about .
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Silicon tetraazide is a white crystalline compound that will detonate at even 0 °C. The pure compound, and also silicon chloride triazide and silicon dichloride diazide contaminated samples, can detonate spontaneously without clear cause.Bretherick's Handbook of Reactive Chemical Hazards, 7th revised edition, Academic Press 2006, The compound is susceptible to hydrolysis. It is soluble in diethylether and benzene. The addition compound with 2,2′-bipyridine is much more stable. A melting point of 212 °C with a melting enthalpy of 110 J·g−1 is recorded. The DSC measurement shows at 265 °C a sharp exothermic reaction with an enthalpy of −2400 J·g−1. Similar results are found for the addition compound with 1,10-phenanthroline.
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The Parisians Pannetier and Binet first prepared the transparent hydrated form of in 1838 via a secret process, sold as a pigment. It is derived from the mineral chromite, . The conversion of chromite to chromia proceeds via , which is reduced with sulfur at high temperatures:Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger, "Chromium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. : + S → + The oxide is also formed by the decomposition of chromium salts such as chromium nitrate, or by the exothermic decomposition of ammonium dichromate. : → + + 4 The reaction has a low ignition temperature of less than 200 °C and is frequently used in “volcano” demonstrations.
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After converting part of this energy to work, the heat engine rejects the remaining energy as heat. Almost all of this heat rejection can be absorbed by the endothermic reduction reaction occurring in the reducer. This arrangement requires the redox reactions to be exothermic and endothermic respectively, but this is normally the case for most metals. Some additional heat exchange with the environment is required to satisfy the second law; theoretically, for a reversible process, the heat exchange is related to the standard state entropy change, ΔSo, of the primary hydrocarbon oxidation reaction as follows: :Qo = ToΔSo However, for most hydrocarbons, ΔSo is a small value and, as a result, an engine of high overall efficiency is theoretically possible.
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The Hammond–Leffler postulate states that the structure of the transition state more closely resembles either the products or the starting material, depending on which is higher in enthalpy. A transition state that resembles the reactants more than the products is said to be early, while a transition state that resembles the products more than the reactants is said to be late. Thus, the Hammond–Leffler Postulate predicts a late transition state for an endothermic reaction and an early transition state for an exothermic reaction. A dimensionless reaction coordinate that quantifies the lateness of a transition state can be used to test the validity of the Hammond–Leffler postulate for a particular reaction.
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In the process of oxidizing food molecules, 2 hydrogen ions, 2 electrons, and an oxygen molecule react to make an exothermic reaction as well as H2O (water). Due to fact that electron transfer is such a broad, common, as well as essential reaction within nature, Marcus's theory has become vital within the field of chemistry. 2H+ \+ 2e− \+ 1/2 O2 → H2O + heat A type of chemical reaction linked to his many studies of electron transfer would be the transfer of an electron between metal ions in different states of oxidation. An example of this type of chemical reaction would be one between a bivalent and a trivalent iron ion in an aqueous solution.
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The lifetime of the deuterium isotopomer is predicted to be much longer due to a greater difficulty of tunneling for deuterium. This molecule's metastability is slated due to electrostatic attraction between HHe+ and F− which increases the barrier to an exothermic breakup. Under pressures over 23 GPa HHeF should be stable. Calculations for coinage metal fluorides include HeCuF as stable, HeAgF is unstable, HeAuF is predicted, and Ag3He with binding energy 1.4 cm−1, Ag4He binding energy 1.85 cm−1, Au3He binding energy 4.91 cm−1, and Au4He binding energy 5.87 cm−1 HeNaO is predicted. Calculation for binary van der Waals helium molecules include HeNe, Li4He binding energy 0.008 cm−1, the Li3He is not stable.
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Calcium chloride is used in concrete mixes to accelerate the initial setting, but chloride ions lead to corrosion of steel rebar, so it should not be used in reinforced concrete. The anhydrous form of calcium chloride may also be used for this purpose and can provide a measure of the moisture in concrete. Calcium chloride is included as an additive in plastics and in fire extinguishers, in CAA as a drainage aid, in blast furnaces as an additive to control scaffolding (clumping and adhesion of materials that prevent the furnace charge from descending), and in fabric softener as a thinner. The exothermic dissolution of calcium chloride is used in self- heating cans and heating pads.
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Vinylsulfonic acid is produced industrially by the alkaline hydrolysis of carbyl sulfate with subsequent acidification of the resulting vinyl sulfonate salt: :Vinylsulfonsäure aus Carbylsulfat The reaction is highly exothermic (reaction enthalpy: 1,675 kJ/kg) and requires exact maintenance of temperature and pH during the hydrolysis. When calcium hydroxide is used as the hydrolysis medium, a solution of calcium vinyl sulfonate is obtained. Acidification of this hydrolysis mixture with sulfuric acid gives vinylsulfonic acid, together with the poorly soluble calcium sulfate. Vinylsulfonic acid also can be prepared by dehydration of isethionic acid with phosphorus pentoxide: :Vinylsulfonsäure via Isethionsäure Vinylsulfonic acid can also be prepared by sulfochlorination of chloroethane, dehydrohalogenation to vinylsulfonyl chloride and subsequent hydrolysis of the acid chloride.
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Thermal energy (T-ENG) is now used for charging up special attacks and restoring the life bar, rather than for survival (represented numerically by the player's HUD in Lost Planet: Extreme Condition and Lost Planet 2) or as currency (used in Lost Planet 3). Players can tap into their T-ENG reserve to release numerous forms of an exothermic (EX-T) blast to deal large amounts of damage to enemies. Armour and weapon upgrades are created from gathering materials (sometimes from enemy remains, similar to Monster Hunter) and require paying vendors with points, which are rewarded after successful missions. Points can also be used to purchase food items that provide various short-term buffs.
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The price of electricity, the power cut and a problem of quantity of row material had obliged to stop the smelting activity. In 2006, the company tested a new process based on an exothermic process. Those tests were a technical success but the second increase of the price of the electricity in December 2005 and the remaining problem of quantity of raw material were not covered by the positive aspects of the new process. Five years after the privatisation, a complete technical and financial audit has been conducted by the Privatisation to see if the conditions of the contract were respected by both parties. It has been decided between the parties, that Phoenix Metal haven‟t any more obligation.
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The Sodium Drop traditionally consisted of a bar of metallic sodium dropped into the Charles River, producing loud explosions due to the rapid exothermic conversion of sodium metal to sodium hydroxide and the ignition of the resulting hydrogen gas. In the past, Sodium Drops occurred sporadically, initiated by impromptu groups of students from various dorms and fraternities. However, in 2007, five volunteers using a boat to clean up trash from the river banks were injured by a small explosion and fire, apparently caused by unreacted sodium residue. MIT quickly donated funds to pay for decontaminating and repairing the boat, although it was not clear at the time who was responsible for the damage.
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The structure of triple flames stabilized on a slot burner discusses the structure of a triple flame that contains three exothermic reaction zones which merge at a "triple point" and shows how these zones have different features. Heat transfer augmentation using a magnetic fluid under the influence of a line dipole describes ferrohydrodynamic convection by examining the relationship between an imposed magnetic field, and the resulting ferrofluid flow and thus temperature distribution. Mathematical model for the cancer stem cell hypothesis discusses how cancers can occur because of mutations in normal stem cells and presents a predictive mathematical model. It is the first work to show mathematically how repeated insult to mature cells increases the risk of cancer.
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Energy diagram An energy diagram can be created based on the enthalpy of reaction of the individual steps. The energy diagram can be used to compare homogeneous and heterogeneous reactions: Due to the high activation energy of the dissociation of nitrogen, the homogeneous gas phase reaction is not realizable. The catalyst avoids this problem as the energy gain resulting from the binding of nitrogen atoms to the catalyst surface overcompensates for the necessary dissociation energy so that the reaction is finally exothermic. Nevertheless, the dissociative adsorption of nitrogen remains the rate determining step: not because of the activation energy, but mainly because of the unfavorable pre-exponential factor of the rate constant.
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The catalyst only serves to increase the rate of reaction as it does not change the position of the thermodynamic equilibrium. The mechanism for the action of the catalyst comprises two steps: # Oxidation of SO2 into SO3 by V5+: #: 2SO2 \+ 4V5+ \+ 2O2− → 2SO3 \+ 4V4+ # Oxidation of V4+ back into V5+ by dioxygen (catalyst regeneration): #: 4V4+ \+ O2 → 4V5+ \+ 2O2− Hot sulfur trioxide passes through the heat exchanger and is dissolved in concentrated H2SO4 in the absorption tower to form oleum: : H2SO4 (l) + SO3 (g) → H2S2O7 (l) Note that directly dissolving SO3 in water is impractical due to the highly exothermic nature of the reaction. Acidic vapor or mists are formed instead of a liquid.
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The bombardier beetle is able to defend itself by directing a spray of hot fluid at an attacker. The mechanism involves a system for mixing hydroquinones and hydrogen peroxide, which react violently to attain a temperature near boiling point, and in some species a nozzle which allows the spray to be directed accurately in any direction. The unique combination of features of the bombardier beetle's defense mechanism—strongly exothermic reactions, boiling-hot fluids, and explosive release—have been claimed by creationists and proponents of intelligent design to be examples of irreducible complexity. Biologists such as the taxonomist Mark Isaak note however that step-by-step evolution of the mechanism could readily have occurred.
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Autothermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane to form syngas. The reaction takes place in a single chamber where the methane is partially oxidized. The reaction is exothermic due to the oxidation. When the ATR uses carbon dioxide the H2:CO ratio produced is 1:1; when the ATR uses steam the H2:CO ratio produced is 2.5:1 The reactions can be described in the following equations, using CO2: : 2 CH4 \+ O2 \+ CO2 → 3 H2 \+ 3 CO + H2O And using steam: : 4 CH4 \+ O2 \+ 2 H2O → 10 H2 \+ 4 CO The outlet temperature of the syngas is between 950-1100 °C and outlet pressure can be as high as 100 bar.
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The reaction is exothermic, and the mixture can reach the boiling point, if external cooling is not applied. The resulting product, diethyl 3,5-dimethylpyrrole-2,4-dicarboxylate, has been called Knorr's Pyrrole ever since. In the Scheme above, R2 = COOEt, and R1 = R3 = Me represent this original reaction. Knorr's pyrrole can be derivatized in a number of useful manners. One equivalent of sodium hydroxide will saponify the 2-ester selectively. Dissolving Knorr's pyrrole in concentrated sulfuric acid, and then pouring the resulting solution into water will hydrolyze the 4-ester group selectively. The 5-methyl group can be variously oxidized to chloromethyl, aldehyde, or carboxylic acid functionality by the use of stoichiometric sulfuryl chloride in glacial acetic acid. Alternatively, the nitrogen atom can be alkylated.
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Solid projectiles may be free-flying (as with bullets and artillery shells) or tethered (as with Taser guns, spearguns and harpoon guns). A large-caliber gun is also referred to as a cannon. The means of projectile propulsion vary according to designs, but are traditionally effected pneumatically by a high gas pressure contained within the barrel tube, produced either through the rapid exothermic combustion of propellants (as with firearms), or by mechanical compression (as with air guns). The high-pressure gas is introduced behind the projectile, pushing and accelerating it down the length of the tube, imparting sufficient launch velocity to sustain its further travel towards the target once the propelling gas ceases acting upon it after it exits the muzzle.
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The process is highly exothermic (ΔH -92 kJ/mol of ethylene oxide reacted) and requires careful control to avoid a potentially disastrous thermal runaway. :ROH + n C2H4O → R(OC2H4)nOH The starting materials are usually primary alcohols as they react ~10-30x faster than do secondary alcohols. Typically 5-10 units of ethylene oxide are added to each alcohol, however ethoxylated alcohols can be more prone to ethoxylation than the starting alcohol, making the reaction difficult to control and leading to the formation of a product with varying repeat unit length (the value of n in the equation above). Better control can be afforded by the use of more sophisticated catalysts, which can be used to generate narrow-range ethoxylates.
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Mixing the two liquid parts causes an exothermic reaction which generates heat and within minutes causes the material to harden, yielding castings or copies in the shape of the mold into which it has been poured. The molds are commonly half-divided (like the hollowed chocolate Easter eggs with candy inside) and a release agent may be used to make removal of the hardened/set resin from the mold easier. The hardened resin casting is removed from the flexible mold and allowed to cool. A Baldwin 6-axle locomotive kit cast in resin in HO Scale Due to aggressive nature of most compounds used for casting and the high temperature of the reaction the mold gradually degrades and loses small details.
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In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exothermic or exergonic if the final state is lower on the energy scale than the initial state; in the case of endothermic reactions the situation is the reverse.
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Autothermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane to form syngas. The reaction takes place in a single chamber where the methane is partially oxidized. The reaction is exothermic due to the oxidation. When the ATR uses carbon dioxide the H2:CO ratio produced is 1:1; when the ATR uses steam the H2:CO ratio produced is 2.5:1 The reactions can be described in the following equations, using CO2: : 2 CH4 \+ O2 \+ CO2 -> 3 H2 \+ 3 CO + H2O And using steam: : 4 CH4 \+ O2 \+ 2 H2O -> 10 H2 \+ 4 CO The outlet temperature of the syngas is between 950-1100 °C and outlet pressure can be as high as 100 bar.
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The regenerator operates at a temperature of about 715 °C and a pressure of about 2.41 bar, hence the regenerator operates at about 0.7 bar higher pressure than the reactor. The combustion of the coke is exothermic and it produces a large amount of heat that is partially absorbed by the regenerated catalyst and provides the heat required for the vaporization of the feedstock and the endothermic cracking reactions that take place in the catalyst riser. For that reason, FCC units are often referred to as being 'heat balanced'. The hot catalyst (at about 715 °C) leaving the regenerator flows into a catalyst withdrawal well where any entrained combustion flue gases are allowed to escape and flow back into the upper part to the regenerator.
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The most important reaction is its carbothermal reduction, which gives iron used in steel-making: : Fe2O3 \+ 3 CO → 2 Fe + 3 CO2 Another redox reaction is the extremely exothermic thermite reaction with aluminium. : 2 Al + Fe2O3 → 2 Fe + Al2O3 This process is used to weld thick metals such as rails of train tracks by using a ceramic container to funnel the molten iron in between two sections of rail. Thermite is also used in weapons and making small-scale cast-iron sculptures and tools. Partial reduction with hydrogen at about 400 °C produces magnetite, a black magnetic material that contains both Fe(III) and Fe(II): :3 Fe2O3 \+ H2 → 2 Fe3O4 \+ H2O Iron(III) oxide is insoluble in water but dissolves readily in strong acid, e.g.
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Division 4.1: Flammable Solid Flammable solids are any of the following four types of materials: #Desensitized Explosives: explosives that, when dry, are Explosives of Class 1 other than those of compatibility group A, which are wetted with sufficient water, alcohol, or plasticizer to suppress explosive properties; and are specifically authorized by name either in the 49CFR 172.101 Table or have been assigned a shipping name and hazard class by the Associate Administrator for Hazardous Materials Safety. #Self-Reactive Materials: materials that are thermally unstable and that can undergo a strongly exothermic decomposition even without participation of oxygen (air). Certain exclusions to this group do apply under 49 CFR. #Generic Types: Division 4.1 self-reactive materials are assigned to a generic system consisting of seven types.
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Sulfur dioxide is the product of the burning of sulfur or of burning materials that contain sulfur: : S + O2 → SO2, ΔH = −297 kJ/mol To aid combustion, liquified sulfur (140–150 °C, 284-302 °F) is sprayed through an atomizing nozzle to generate fine drops of sulfur with a large surface area. The reaction is exothermic, and the combustion produces temperatures of 1000–1600 °C (1832–2912 °F). The significant amount of heat produced is recovered by steam generation that can subsequently be converted to electricity. The combustion of hydrogen sulfide and organosulfur compounds proceeds similarly. For example: : 2 H2S + 3 O2 → 2 H2O + 2 SO2 The roasting of sulfide ores such as pyrite, sphalerite, and cinnabar (mercury sulfide) also releases SO2:Shriver, Atkins.
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Formed in 1977, the Design Institute for Emergency Relief Systems was a consortium of 29 companies under the auspices of the American Institute of Chemical Engineers (AIChE) that developed methods for the design of emergency relief systems to handle runaway reactions. Its purpose was to develop the technology and methods needed for sizing pressure relief systems for chemical reactors, particularly those in which exothermic reactions are carried out. Such reactions include many classes of industrially important processes including polymerizations, nitrations, diazotizations, sulphonations, epoxidations, aminations, esterifications, neutralizations, and many others. Pressure relief systems can be difficult to design, not least because what is expelled can be gas/vapor, liquid, or a mixture of the two – just as with a can of carbonated drink when it is suddenly opened.
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Born–Haber cycles are used primarily as a means of calculating lattice energy (or more precisely enthalpyThe difference between energy and enthalpy is very small and the two terms are interchanged freely in this article.), which cannot otherwise be measured directly. The lattice enthalpy is the enthalpy change involved in the formation of an ionic compound from gaseous ions (an exothermic process), or sometimes defined as the energy to break the ionic compound into gaseous ions (an endothermic process). A Born–Haber cycle applies Hess's law to calculate the lattice enthalpy by comparing the standard enthalpy change of formation of the ionic compound (from the elements) to the enthalpy required to make gaseous ions from the elements. This latter calculation is complex.
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The process can be divided into five stages: # Combining of sulfur and oxygen (O2) to form sulfur dioxide # Purifying the sulfur dioxide in a purification unit # Adding an excess of oxygen to sulfur dioxide in the presence of the catalyst vanadium pentoxide at 450 °C and 1-2 atm # The sulfur trioxide formed is added to sulfuric acid which gives rise to oleum (disulfuric acid) # The oleum is then added to water to form sulfuric acid which is very concentrated. #As this process is an exothermic reaction so the temperature should be as low as possible. The yield has been found to be maximum at about 410 - 450° C. Purification of the air and sulfur dioxide (SO2) is necessary to avoid catalyst poisoning (i.e. removing catalytic activities).
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Since its discovery in 1994, A. caldus has been found to have a significant practical application in the industrial field of biomining and mineral biotechnology, contributing to the enhanced recovery of desired minerals from rocks known as ores. Metals such as gold have been recovered from ores which contain pyrite (also known as fool's gold) and arsenopyrite, two sulfide minerals that are often associated with considerable amounts of this precious metal. Biomining refers to both biooxidation, where the sulfide mineral surrounding the desired metal is oxidized to expose the metal of interest, and bioleaching, where the sulfide mineral is solubilized to obtain the metal of interest. Due to the exothermic nature of bioleaching, the thermophilic nature of A. caldus allows for less cooling and quicker rates of bioleaching overall.
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Zones in a candle flame Color and temperature of a flame are dependent on the type of fuel involved in the combustion, as, for example, when a lighter is held to a candle. The applied heat causes the fuel molecules in the candle wax to vaporize (If this process happens in inert atmosphere without oxidizer, it's called pyrolysis). In this state they can then readily react with oxygen in the air, which gives off enough heat in the subsequent exothermic reaction to vaporize yet more fuel, thus sustaining a consistent flame. The high temperature of the flame causes the vaporized fuel molecules to decompose, forming various incomplete combustion products and free radicals, and these products then react with each other and with the oxidizer involved in the reaction.
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A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor e^{-E/kT} – that is the probability of a molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation. The activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.
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A simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. This reaction releases 242kJ/mol of heat and reduces the enthalpy accordingly (at constant temperature and pressure): : 2(g) + (g) → 2(g) Combustion of an organic fuel in air is always exothermic because the double bond in O is much weaker than other double bonds or pairs of single bonds, and therefore the formation of the stronger bonds in the combustion products and results in the release of energy. The bond energies in the fuel play only a minor role, since they are similar to those in the combustion products; e.g., the sum of the bond energies of CH is nearly the same as that of .
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But at higher temperatures, calcium sulfate will release oxygen and act as an oxidizing agent. This property is used in aluminothermy. In contrast to most minerals, which when rehydrated simply form liquid or semi-liquid pastes, or remain powdery, calcined gypsum has an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice: :CaSO4 · H2O + H2O -> CaSO4 · 2 H2O This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement.
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Sodium bisulfate is produced as an intermediate in the Mannheim process, an industrial process involving the reaction of sodium chloride and sulfuric acid: :NaCl + H2SO4 → HCl + NaHSO4 This step is highly exothermic. The liquid sodium bisulfate is sprayed and cooled so that it forms a solid bead. The hydrogen chloride gas is dissolved in water to produce hydrochloric acid as a useful coproduct of the reaction. Although not of commercial interest, sodium bisulfate can be generated as a byproduct of the production of many other mineral acids via the reaction of their sodium salts with an excess of sulfuric acid: :NaX + H2SO4 → NaHSO4 \+ HX ( X− = CN−, NO3−, ClO4−) The acids HX produced have a lower boiling point than the reactants and are separated from the reaction mixture by distillation.
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The PROX process allows for the reaction of CO with oxygen, reducing CO concentration from approximately 0.5-1.5% in the feed gas to less than 10 ppm. :2CO + O2 -> 2CO2 Due to the prevalent presence of hydrogen in the feed gas, the competing, undesired combustion of hydrogen will also occur to some degree: :2H2 \+ O2 -> 2H2O The selectivity of the process is a measure of the quality of the reactor, and is defined as the ratio of consumed carbon monoxide to the total of consumed hydrogen and carbon monoxide. The disadvantage of this technology is its very strong exothermic nature, coupled with a very narrow optimal operation temperature window, and is best operated between 353 and 450 K, yielding a hydrogen loss of around one percent. Effective cooling is therefore required.
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All such units and equipment should also be checked for materials compatibility to ensure they can withstand long-term exposure to the chemicals they will come in contact with. Any closed system in a plant which has a means of pressurizing possibly beyond the rating of its equipment, such as heating, exothermic reactions, or certain pumps or compressors, should have an appropriately sized pressure relief valve included to prevent overpressurization for safety. Frequently all of these parameters (temperatures, pressures, flow, etc.) are exhaustively analyzed in combination through a Hazop or fault tree analysis, to ensure that the plant has no known risk of serious hazard. Within any constraints the plant is subject to, design parameters are optimized for good economic performance while ensuring safety and welfare of personnel and the surrounding community.
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Lithium deuteride, in the form of lithium-7 deuteride, is a good moderator for nuclear reactors, because deuterium (2H) has a lower neutron absorption cross-section than ordinary hydrogen (1H) does, and the cross- section for 7Li is also low, decreasing the absorption of neutrons in a reactor. 7Li is preferred for a moderator because it has a lower neutron capture cross-section, and it also forms less tritium (3H) under bombardment with neutrons. The corresponding lithium-6 deuteride, 6Li2H, or 6LiD, is the primary fusion fuel in thermonuclear weapons. In hydrogen warheads of the Teller–Ulam design, a nuclear fission trigger explodes to heat and compress the lithium-6 deuteride, and to bombard the 6LiD with neutrons to produce 3H (tritium) in an exothermic reaction: 6Li2H + n → 4He + 3H.
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Runaway thermonuclear reactions can occur in stars when nuclear fusion is ignited in conditions under which the pressure exerted by overlying layers of the star greatly exceeds thermal pressure, a situation that makes possible rapid increases in temperature. Such a scenario may arise in stars containing degenerate matter, in which electron degeneracy pressure rather than normal thermal pressure does most of the work of supporting the star against gravity, and in stars undergoing implosion. In all cases, the imbalance arises prior to fusion ignition; otherwise, the fusion reactions would be naturally regulated to counteract temperature changes and stabilize the star. When thermal pressure is in equilibrium with overlying pressure, a star will respond to the increase in temperature and thermal pressure due to initiation of a new exothermic reaction by expanding and cooling.
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As atomic carbon is an electron-deficient species, it spontaneously autopolymerises in its pure form, or converts to an adduct upon treatment with a Lewis acid or base. Oxidation of atomic carbon gives carbon monoxide, whereas reduction gives λ2-methane. Non-metals, including oxygen, strongly attack atomic carbon, forming divalent carbon compounds: :2 [C] + → 2 CO Atomic carbon is highly reactive, most reactions are very exothermic. They are generally carried out in the gas phase at liquid nitrogen temperatures (77 K). Typical reactions with organic compounds include:Reactive Intermediate Chemistry, Robert A. Moss, Matthew S. Platz and Maitland Jones Jr., Wiley-Blackwell, (2004), :Insertion into a C-H bond in alkanes to form a carbene :Deoxygenation of carboxyl groups in ketones and aldehydhdes to form a carbene, 2-butanone forming 2-butanylidene.
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In the case of neutrons carrying most of the practical energy, as is the case in the D-T fuel, this neutron energy is normally captured in a "blanket" of lithium that produces more tritium that is used to fuel the reactor. Due to various exothermic and endothermic reactions, the blanket may have a power gain factor MR. MR is typically on the order of 1.1 to 1.3, meaning it produces a small amount of energy as well. The net result, the total amount of energy released to the environment and thus available for energy production, is referred to as PR, the net power output of the reactor. The blanket is then cooled and the cooling fluid used in a heat exchanger driving conventional steam turbines and generators.
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The board noted that a silver-plated copper wire, running through an environmental control unit near the center couch, had become stripped of its Teflon insulation and abraded by repeated opening and closing of a small access door. This weak point in the wiring also ran near a junction in an ethylene glycol/water cooling line that had been prone to leaks. The electrolysis of ethylene glycol solution with the silver anode was discovered at the Manned Spacecraft Center on May 29, 1967, to be a hazard capable of causing a violent exothermic reaction, igniting the ethylene glycol mixture in the Command Module's pure oxygen atmosphere. Experiments at the Illinois Institute of Technology confirmed the hazard existed for silver-plated wires, but not for copper-only or nickel-plated copper.
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The following reactions describe the methanation of carbon monoxide and carbon dioxide respectively: :CO + 3H2 -> CH4 + H2O -206 kJ/mol :CO2 + 4H2 -> CH4 + 2 H2O -164 kJ/mol The methanation reactions are classified as exothermic and their energy of formations are listed. There is disagreement on whether the CO2 methanation occurs by first associatively adsorbing an adatom hydrogen and forming oxygen intermediates before hydrogenation or dissociating and forming a carbonyl before being hydrogenated. CO methanation is believed to be methanated through a dissociative mechanism where the carbon oxygen bond is broken before hydrogenation with an associative mechanism only being observed at high H2 concentrations. Methanation reaction over different carried metal catalysts including Ni, Ru and Rh has been widely investigated for the production of CH4 from syngas and other power to gas initiatives.
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When accelerated to high enough speeds, nuclei can overcome this electrostatic repulsion and be brought close enough such that the attractive nuclear force is greater than the repulsive Coulomb force. The strong force grows rapidly once the nuclei are close enough, and the fusing nucleons can essentially "fall" into each other and the result is fusion and net energy produced. The fusion of lighter nuclei, which creates a heavier nucleus and often a free neutron or proton, generally releases more energy than it takes to force the nuclei together; this is an exothermic process that can produce self-sustaining reactions. Energy released in most nuclear reactions is much larger than in chemical reactions, because the binding energy that holds a nucleus together is greater than the energy that holds electrons to a nucleus.
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Thus, the generated substitute natural gas can be injected in the entire German natural gas network without limitations.DIN EN 16723-2:2017-10 - Erdgas und Biomethan zur Verwendung im Transportwesen und Biomethan zur Einspeisung ins Erdgasnetz As a cooling medium for the exothermic reaction boiling water is used at up to 300 °C, which corresponds to a water vapour pressure of about 87 bar. The SOEC works with a pressure of up to 15 bar, steam conversions of up to 90% and generates one standard cubic meter of hydrogen from 3.37 kWh of electricity as feed for the methanation. The technological maturity of Power to Gas is evaluated in the European 27 partner project STORE&GO;, which has started in March 2016 with a runtime of four years.
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The acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction; the pKa value is directly proportional to the standard Gibbs free energy change for the reaction. The value of the pKa changes with temperature and can be understood qualitatively based on Le Châtelier's principle: when the reaction is endothermic, Ka increases and pKa decreases with increasing temperature; the opposite is true for exothermic reactions. The value of pKa also depends on molecular structure of the acid in many ways. For example, Pauling proposed two rules: one for successive pKa of polyprotic acids (see Polyprotic acids below), and one to estimate the pKa of oxyacids based on the number of =O and −OH groups (see Factors that affect pKa values below).
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Readily combustible solids are powdered, granular, or pasty substances which are dangerous if they can be easily ignited by brief contact with an ignition source, such as a burning match, and if the flame spreads rapidly. it is further divided into • flammable solids, • polymerizing substances # self-reactive substances, are thermally unstable solids liable to undergo a strongly exothermic thermal decomposition even without participation of oxygen (air), other than materials classified as explosive, organic peroxides or as oxidizing. # pyrophoric substance more colloquially described as spontaneously combusting substances are those solids or liquids that even in small quantities are liable to ignite within five minutes after coming into contact with air. Substances and mixtures of this hazard class are assigned to a single hazard category on the basis of the outcome of the UN Test N.2.
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During cosmic times, nuclear reactions re-arrange the nucleons that were left behind from the big bang (in the form of isotopes of hydrogen and helium, and traces of lithium, beryllium, and boron) to other isotopes and elements as we find them today (see graph). The driver is a conversion of nuclear binding energy to exothermic energy, favoring nuclei with more binding of their nucleons - these are then lighter as their original components by the binding energy. The most tightly-bound nucleus from symmetric matter of neutrons and protons is 56Ni. The release of nuclear binding energy is what allows stars to shine for up to billions of years, and may disrupt stars in stellar explosions in case of violent reactions (such as 12C+12C fusion for thermonuclear supernova explosions).
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For the oxidation of each metal, the dominant contribution to the entropy change (ΔS) is the removal of mol , so that ΔS is negative and roughly equal for all metals. The slope of the plots is therefore positive for all metals, with ΔG always becoming more negative with lower temperature, and the lines for all the metal oxides are approximately parallel. Since these reactions are exothermic, they always become feasible at lower temperatures. At a sufficiently high temperature, the sign of ΔG may invert (becoming positive) and the oxide can spontaneously reduce to the metal, as shown for Ag and Cu. For oxidation of carbon, the red line is for the formation of CO: C(s) + (g) → CO(g) with an increase in the number of moles of gas, leading to a positive ΔS and a negative slope.
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In this mode the sample will be housed in a non-reactive crucible (often Gold, or Gold plated steel), and which will be able to withstand pressure (typically up to 100 bar). The presence of an exothermic event can then be used to assess the stability of a substance to heat. However, due to a combination of relatively poor sensitivity, slower than normal scan rates (typically 2–3°/min - due to much heavier crucible) and unknown activation energy, it is necessary to deduct about 75–100 °C from the initial start of the observed exotherm to suggest a maximum temperature for the material. A much more accurate data set can be obtained from an adiabatic calorimeter, but such a test may take 2–3 days from ambient at a rate of 3 °C increment per half hour.
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In 1928, Khariton decided to take up the residence in (Germany) to be near his mother, but was appalled and frightened by the political propaganda of the Nazi Party in Germany; therefore returning to Soviet Union while his mother left for Palestine. In 1931, he joined the Institute of Chemical Physics and eventually headed the explosion laboratory until 1946, working closely with another Russian physicist Yakov Borisovich Zel'dovich, on exothermic chemical chain reactions.. In 1935, he received his doctorate in physical and mathematical sciences. During this period, Khariton and Zel'dovich conducted experiments on the chain reactions of uranium. In August 1939, Zel'dovich, Khariton and Aleksandr Leipunskii delivered papers on the theoretical process behind nuclear fission chain reactions at a conference in Kharkiv, Ukraine; this was the last pre-war discussion of chain reactions in the USSR.
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George E. Pellissier, engineer and manager for the Holyoke Street Railway as well as the Goldschmidt Thermit Company As a transportation system, the railway also held at least one unprecedented piece of technology prior to its numerous competitors in the early 20th century- thermite welding. During the 1890s in Germany, Hans Goldschmidt developed the modern process for exothermic welding for railways. This process, now an international standard in railway construction, was first used commercially in tram lines in Essen, Germany in 1899. Over the next several years other cities including Leeds and Singapore would adopt this construction method, and in 1904 its inventor would open the Goldschmidt Thermit Company offices in New York City. While development of this process continued, an engineering student at Worcester Polytechnic Institute, George E. Pellissier (1878-1961)Stephan Kallee: George E. Pellissier.
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Mixing ethanol and water is exothermic, with up to 777 J/mol being released at 298 K. Mixtures of ethanol and water form an azeotrope at about 89 mole-% ethanol and 11 mole-% water or a mixture of 95.6 percent ethanol by mass (or about 97% alcohol by volume) at normal pressure, which boils at 351K (78 °C). This azeotropic composition is strongly temperature- and pressure-dependent and vanishes at temperatures below 303 K. Hydrogen bonding in solid ethanol at −186 °C Hydrogen bonding causes pure ethanol to be hygroscopic to the extent that it readily absorbs water from the air. The polar nature of the hydroxyl group causes ethanol to dissolve many ionic compounds, notably sodium and potassium hydroxides, magnesium chloride, calcium chloride, ammonium chloride, ammonium bromide, and sodium bromide. Sodium and potassium chlorides are slightly soluble in ethanol.
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In future designs, the oxygen by-product may be combined with renewable natural gasThe first industrial PtG plant – Audi e-gas as driver for the energy turnaround in the oxidative coupling of methane to ethylene:Olah, G., Molnar, A. “Hydrocarbon Chemistry” John Wiley & Sons, New York, 2003. . : 2 + -> \+ 2 The reaction is exothermic (∆H = -280 kJ/mol) and occurs at high temperatures (750–950 ˚C). The yield of the desired products is reduced by non-selective reactions of methyl radicals with the reactor surface and oxygen, which produces carbon monoxide and carbon dioxide by-products. Another ethylene production initiative developed by the European Commission through the Seventh Framework Programme for Research and Technological Development is the OCMOL process, which is the Oxidative Coupling of Methane (OCM) and simultaneous Reforming of Methane (RM) in a fully integrated reactor.
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More ammonia would be produced if the reaction were run at a lower temperature, but a lower temperature also lowers the rate of the process, so, in practice (the Haber process) the temperature is set at a compromise value that allows ammonia to be made at a reasonable rate with an equilibrium concentration that is not too unfavorable. In exothermic reactions, an increase in temperature decreases the equilibrium constant, K, whereas in endothermic reactions, an increase in temperature increases K. Le Chatelier's principle applied to changes in concentration or pressure can be understood by giving K a constant value. The effect of temperature on equilibria, however, involves a change in the equilibrium constant. The dependence of K on temperature is determined by the sign of ΔH. The theoretical basis of this dependence is given by the Van 't Hoff equation.
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This oxygen supports combustion; it combines with fuels such as gasoline, alcohol, diesel fuel, propane, or CNG to produce carbon dioxide and water vapor, along with heat, which causes the former two products of combustion to expand and exert pressure on pistons, driving the engine. Nitrous oxide is stored as a liquid in tanks, but is a gas under atmospheric conditions. When injected as a liquid into an inlet manifold, the vaporization and expansion causes a reduction in air/fuel charge temperature with an associated increase in density, thereby increasing the cylinder's volumetric efficiency. As the decomposition of N2O into oxygen and nitrogen gas is exothermic and thus contributes to a higher temperature in the combustion engine, the decomposition increases engine efficiency and performance, which is directly related to the difference in temperature between the unburned fuel mixture and the hot combustion gasses produced in the cylinders.
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Figure 12: Asymmetric glyoxylate-ene reaction catalyzed by a chiral titanium complex Since both (R)- and (S)-BINOL are commercially available in optically pure form, this asymmetric process allows the synthesis of both enantiomers of α-hydroxy esters and their derivatives. However, this method is only applicable to 1,1-disubstituted olefins, due to the modest Lewis acidity of the titanium-BINOL complex. As shown in Figure 13, Corey and co-workers propose an early transition state for this reaction, with the goal of explaining the high enantioselectivity observed (assuming that the reaction is exothermic as calculated from standard bond energies). Even if the structure of the active catalyst is not known, Corey’s model proposes the following: the aldehyde is activated by complexation with the chiral catalyst (R)-BINOL-TiX2 by the formyl lone electron pair syn to the formyl hydrogen to form a pentacoordinate Ti structure.
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The thermonuclear burn would produce (like the fission fuel in the primary) pulsations (generations) of high-energy neutrons with an average temperature of 14 MeV through Jetter's cycle. The cycle is a combination of endothermic and exothermic neutronic reactions involving lithium and deuterium/tritium. The reaction's neutronicity was estimated at ≈0.885 (for a Lawson criterion of ≈1.5). These figures do not count the Li isotope, where the LiD has a neutronicity of ≈0.835 and, along with the cross-sections, were given as group averages from about 2.40 to approximately 2.55 MeV and from 14.0 to 14.1 MeV; the small power group is not statistically present (see also Nuclear fusion). As SHRIMP, along with the RUNT I and ALARM CLOCK were to be high-yield shots required to assure the thermonuclear “emergency capability”, their fusion fuel may have been spiked with additional tritium, in the form of LiT.
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Michler’s ketone is an intermediate in the synthesis of dyes and pigments for paper, textiles, and leather. Condensation with various aniline derivatives gives several of the dyes called methyl violet, such as crystal violet. Condensation of Michler's ketone with N-phenyl-1-naphthylamine gives the dye Victoria Blue B (CAS#2580-56-5, CI Basic Blue 26), which is used for coloring paper and producing pastes and inks for ballpoint pens. Michler’s ketone is commonly used as an additive in dyes and pigments as a sensitizer for photoreactions because of its absorption properties. Michler’s ketone is an effective sensitizer provided energy transfer is exothermic and the concentration of the acceptor is sufficiently high to quench the photoreaction of Michler’s ketone with itself. Specifically Michler’s ketone absorbs intensely at 366 nm and effectively sensitizes photochemical reactions such as the dimerization of butadiene to give 1,2-divinylcyclobutane.
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This nuclear reaction 14N (n,p) 14C continually happens in the Earth's atmosphere, forming equilibrium amounts of the radionuclide 14C. Most (n,p) reactions have threshold neutron energies below which the reaction cannot take place as a result of the charged particle in the exit channel requiring energy (usually more than a MeV) to overcome the Coulomb barrier experienced by the emitted proton. The (n,p) nuclear reaction 14N (n,p) 14C is an exception to this rule, and is exothermic – it can take place at all incident neutron energies. The 14N (n,p) 14C nuclear reaction is responsible for most of the radiation dose delivered to the human body by thermal neutrons – these thermal neutrons are absorbed by the nitrogen 14N in proteins, causing a proton to be emitted; the emitted proton deposits its kinetic energy over a very short distance in the body tissue, thereby depositing radiation dose.
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When considering whether a specific nuclear transmutation, a reaction or a decay, is energetically allowed, one only needs to sum the masses of the initial nucleus/nuclei and subtract from that value the sum of the masses of the product particles. If the result, or Q-value, is positive, then the transmutation is allowed, or exothermic because it releases energy, and if the Q-value is a negative quantity, then it is endothermic as at least that much energy must be added to the system before the transmutation may proceed. For example, to determine if 12C, the most common isotope of carbon, can undergo proton emission to 11B, one finds that about 16 MeV must be added to the system for this process to be allowed. While Q-values can be used to describe any nuclear transmutation, for particle decay, the particle separation energy quantity S, is also used, and it is equivalent to the negative of the Q-value.
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A firearm is a barreled ranged weapon that inflicts damage on targets by launching one or more projectiles driven by rapidly expanding high-pressure gas produced by exothermic combustion (deflagration, hence the word stem "fire-") of a chemical propellant, historically black powder, now smokeless powder. In the military, firearms are categorized into "heavy" and "light" weapons regarding their portability by foot soldiers. The subset of light firearms that use kinetic projectiles and are compact enough to be operated to full capacity by a single infantryman (rather than being crew-served) are also referred to as "small arms", a hyponym to which the word "firearm" are often referring in common usage. Such firearms include handguns such as revolvers, pistols and derringers, and long guns such as rifles (of which there are many subtypes such as anti-material rifles, sniper rifles, designated marksman rifles, battle rifles, assault rifles and carbines), shotguns, submachine guns/personal defense weapons, squad automatic weapons and light machine guns.
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The mass of a neutron cannot be directly determined by mass spectrometry due to lack of electric charge. However, since the masses of a proton and of a deuteron can be measured with a mass spectrometer, the mass of a neutron can be deduced by subtracting proton mass from deuteron mass, with the difference being the mass of the neutron plus the binding energy of deuterium (expressed as a positive emitted energy). The latter can be directly measured by measuring the energy (B_d) of the single gamma photon emitted when neutrons are captured by protons (this is exothermic and happens with zero-energy neutrons), plus the small recoil kinetic energy (E_{rd}) of the deuteron (about 0.06% of the total energy). :m_n= m_d - m_p + B_d - E_{rd} The energy of the gamma ray can be measured to high precision by X-ray diffraction techniques, as was first done by Bell and Elliot in 1948.
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Black snake experiment Three chemical reactions occur when the snake is lit. Sodium bicarbonate breaks down into sodium carbonate, water vapor, and carbon dioxide: : 2 NaHCO3(s) → Na2CO3(s) + H2O(g) + CO2(g) Burning sucrose or ethanol (reaction with oxygen in the air) produces carbon dioxide gas and water vapor: : C12H22O11(s) + 12 O2(g) → 12 CO2(g) + 11 H2O(g) : C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(g) Some of the sucrose does not burn, but merely decomposes at the high temperature, giving off elemental carbon and water vapor: : C12H22O11(s) → 12 C(s) + 11 H2O(g) The carbon in the reaction makes the snake black. The overall process is exothermic enough that the water produced in the reactions is vaporized. This steam, in addition to the carbon dioxide product, makes the snake lightweight and airy and allows it to grow to a large size from a comparably small amount of starting material.
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Another important use of vanadium(V) oxide is in the manufacture of sulfuric acid, an important industrial chemical with an annual worldwide production of 165 million metric tons in 2001, with an approximate value of US$8 billion. Vanadium(V) oxide serves the crucial purpose of catalysing the mildly exothermic oxidation of sulfur dioxide to sulfur trioxide by air in the contact process: :2 SO2 \+ O2 2 SO3 The discovery of this simple reaction, for which V2O5 is the most effective catalyst, allowed sulfuric acid to become the cheap commodity chemical it is today. The reaction is performed between 400 and 620 °C; below 400 °C the V2O5 is inactive as a catalyst, and above 620 °C it begins to break down. Since it is known that V2O5 can be reduced to VO2 by SO2, one likely catalytic cycle is as follows: :SO2 \+ V2O5 → SO3 \+ 2VO2 followed by :2VO2 +½O2 → V2O5 It is also used as catalyst in the selective catalytic reduction (SCR) of NOx emissions in some power plants.
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Phosphorus pentoxide is a potent dehydrating agent as indicated by the exothermic nature of its hydrolysis: :P4O10 \+ 6 H2O → 4 H3PO4 (–177 kJ) However, its utility for drying is limited somewhat by its tendency to form a protective viscous coating that inhibits further dehydration by unspent material. A granular form of P4O10 is used in desiccators. Consistent with its strong desiccating power, P4O10 is used in organic synthesis for dehydration. The most important application is for the conversion of primary amides into nitriles:Meier, M. S. "Phosphorus(V) Oxide" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. . :P4O10 \+ RC(O)NH2 → P4O9(OH)2 \+ RCN The indicated coproduct P4O9(OH)2 is an idealized formula for undefined products resulting from the hydration of P4O10. Alternatively, when combined with a carboxylic acid, the result is the corresponding anhydride: :P4O10 \+ RCO2H → P4O9(OH)2 \+ [RC(O)]2O The "Onodera reagent", a solution of P4O10 in DMSO, is employed for the oxidation of alcohols.
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As a result of the exothermic reaction of hydrothermal carbonization, about 3/8 of the calorific value of the biomass based on the dry mass is released (with a high lignin, resin and / or oil content at least 1/4). If the process is managed properly, it is possible to use this waste heat from wet biomass to produce dry biocoal and to use some of the converted energy for energy generation. In a large-scale technical implementation of hydrothermal carbonization of sewage sludge, it has been shown that about 20% of the fuel energy content contained in 90% end-dried HTC coal is required to heat the process. Furthermore, approximately 5% of the generated energy content is necessary for electrical operation of the plant. It has proved particularly beneficial in the case of the HTC process that, with mechanical dehydration, more than 60% of the dry substance content can be achieved in the raw carbon, and thus the energy and equipment expenditure for the final drying of the coal is low compared to conventional drying methods of these slurries.
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The stoichiometric ratio of oxidiser and fuel is 2:1, for an oxygen:methane engine: :CH4 + 2O2 -> CO2 + 2H2O However, one pass through the Sabatier reactor produces a ratio of only 1:1. More oxygen may be produced by running the water-gas shift reaction (WGSR) in reverse (RWGS), effectively extracting oxygen from the atmosphere by reducing carbon dioxide to carbon monoxide. Another option is to make more methane than needed and pyrolyze the excess of it into carbon and hydrogen (see above section), where the hydrogen is recycled back into the reactor to produce further methane and water. In an automated system, the carbon deposit may be removed by blasting with hot Martian CO2, oxidizing the carbon into carbon monoxide, which is vented. A fourth solution to the stoichiometry problem would be to combine the Sabatier reaction with the reverse water-gas shift (RWGS) reaction in a single reactor as follows: :3CO2 + 6H2 -> CH4 + 2CO + 4H2O This reaction is slightly exothermic, and when the water is electrolyzed, an oxygen to methane ratio of 2:1 is obtained.
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The combustion of ammonia to nitrogen and water is exothermic: The standard enthalpy change of combustion, ΔH°c, expressed per mole of ammonia and with condensation of the water formed, is −382.81 kJ/mol. Dinitrogen is the thermodynamic product of combustion: all nitrogen oxides are unstable with respect to N2 and O2, which is the principle behind the catalytic converter. Nitrogen oxides can be formed as kinetic products in the presence of appropriate catalysts, a reaction of great industrial importance in the production of nitric acid: A subsequent reaction leads to NO2: The combustion of ammonia in air is very difficult in the absence of a catalyst (such as platinum gauze or warm chromium(III) oxide), due to the relatively low heat of combustion, a lower laminar burning velocity, high auto-ignition temperature, high heat of vaporization, and a narrow flammability range. However, recent studies have shown that efficient and stable combustion of ammonia can be achieved using swirl combustors, thereby rekindling research interest in ammonia as a fuel for thermal power production.
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This oxide layer is the capacitor dielectric. This process of oxide formation is carried out in two reaction steps whereby the oxygen for this reaction has to come from the electrolyte.Nichicon, "General Descriptions of Aluminum Electolytic Capacitors, 1-3 Dielectric (Aluminum Oxide Layer)" PDF First, a strongly exothermic reaction transforms the metallic aluminum (Al) into aluminum hydroxide, Al(OH)3: : 2 Al + 6 H2O → 2 Al(OH)3 \+ 3 H2 ↑ This reaction is accelerated by a high electric field and high temperatures, and is accompanied by a pressure buildup in the capacitor housing caused by the released hydrogen gas. The gel-like aluminum hydroxide Al(OH)3, also called alumina trihydrate (ATH), is converted via a second reaction step (usually slowly over a few hours at room temperature, more rapidly in a few minutes at higher temperatures) into aluminum oxide, Al2O3: :2 Al(OH)3 → 2 AlO(OH) + 2 H2O → Al2O3 \+ 3 H2O The aluminum oxide serves as dielectric and also protects the metallic aluminum against aggressive chemical reactions from the electrolyte.
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When the beetle feels threatened it opens a valve which allows the aqueous solution from the reservoir to reach the vestibule. The catalases lining the vestibule wall facilitate the decomposition of hydrogen peroxide, as in the following theoretical reaction: :H2O2(aq) -> H2O(l) + 1/2O2(g) The peroxidase enzymes facilitate the oxidation of the hydroquinones into quinones (benzene-1,4-diol into 1,4-benzoquinone and analogously for methylhydroquinone), as in the following theoretical reaction: :C6H4(OH)2(aq) -> C6H4O2(aq) + H2(g) The known net reaction, which further accounts for the theoretical reaction of the H2(g) and 1/2O2(g) products of the previous reactions, is: :C6H4(OH)2(aq) + H2O2(aq) -> C6H4O2(aq) + 2H2O(l) Benzoquinone This reaction is very exothermic, and the released energy raises the temperature of the mixture to near 100 °C, vaporizing about a fifth of it. The resultant pressure buildup forces the entrance valves from the reactant storage chambers to close, thus protecting the beetle's internal organs. The boiling, foul-smelling liquid is expelled violently through an outlet valve, with a loud popping sound.
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The formation of an alkali metal nitride would consume the ionisation energy of the alkali metal (forming M+ ions), the energy required to break the triple bond in N2 and the formation of N3− ions, and all the energy released from the formation of an alkali metal nitride is from the lattice energy of the alkali metal nitride. The lattice energy is maximised with small, highly charged ions; the alkali metals do not form highly charged ions, only forming ions with a charge of +1, so only lithium, the smallest alkali metal, can release enough lattice energy to make the reaction with nitrogen exothermic, forming lithium nitride. The reactions of the other alkali metals with nitrogen would not release enough lattice energy and would thus be endothermic, so they do not form nitrides at standard conditions. Sodium nitride (Na3N) and potassium nitride (K3N), while existing, are extremely unstable, being prone to decomposing back into their constituent elements, and cannot be produced by reacting the elements with each other at standard conditions.. 'Elusive Binary Compound Prepared' Chemical & Engineering News 80 No. 20 (20 May 2002) Steric hindrance forbids the existence of rubidium or caesium nitride.
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