WordNet

(mechanics) the equal and opposite force that is produced when any force is applied to a body; "every action has an equal and opposite reaction"
a response that reveals a persons feelings or attitude; "he was pleased by the audiences reaction to his performance"; "John feared his mothers reaction when she saw the broken lamp"
a bodily process occurring due to the effect of some antecedent stimulus or agent; "a bad reaction to the medicine"; "his responses have slowed with age" (同)response
doing something in opposition to another way of doing it that you dont like; "his style of painting was a reaction against cubism"
an idea evoked by some experience; "his reaction to the news was to start planning what to do"
extreme conservatism in political or social matters; "the forces of reaction carried the election"
(of a chemical reaction or compound) occurring or formed with the liberation of heat (同)exothermal, heat-releasing
a compound that gives off heat during its formation and absorbs heat during its decomposition

PrepTutorEJDIC

{名}(…に対する)『反応』《+『to』+『名』》 / 〈U〉(…に対する)(政治的・社会的な)『反動』,逆コース《+『against』+『名』》 / 〈U〉〈C〉化学反応,化学変化 / 〈U〉〈C〉(物理学で)反作用
(化学変化で)放熱の,発熱の

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/08/03 07:07:37」(JST)

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An exothermic thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.

An exothermic reaction is a chemical reaction that releases energy in the form of light or heat. It is the opposite of an endothermic reaction.^[1]

Expressed in a chemical equation: reactants → products + energy

Overview[edit source | edit]

An exothermic reaction is a chemical or physical reaction that is done by the release of heat. It gives out energy to its surroundings. The energy needed for the reaction to occur is less than the total energy released.^[2]

When using a calorimeter, the change in heat of the calorimeter is equal to the opposite of the change in heat of the system. This means that when the medium in which the reaction is taking place gains heat, the reaction is exothermic.

The absolute amount of energy in a chemical system is extremely difficult to measure or calculate. The enthalpy change, ΔH, of a chemical reaction is much easier to measure and calculate. A bomb calorimeter is very suitable for measuring the energy change, ΔH, of a combustion reaction. Measured and calculated ΔH values are related to bond energies by:

ΔH = energy used in bond breaking reactions − energy released in bond making products

An energy profile of an exothermic reaction

by definition the enthalpy change has a negative value:

ΔH < 0

in an exothermic reaction, gives a negative value for ΔH, since a larger value (the energy released in the reaction) is subtracted from a smaller value (the energy used for the reaction). For example, when hydrogen burns:

2H₂ (g) + O₂ (g) → 2H₂O (g)

ΔH = −483.6 kJ/mol of O₂ ^[3]

Examples of exothermic reactions[edit source | edit]

Combustion reactions of fuels
Neutralization reactions such as direct reaction of acid and base
Adding concentrated acid to water {neutralization}
Burning of a substance
Adding water to anhydrous copper(II) sulfate
The thermite reaction
Reactions taking place in a self-heating can based on lime and aluminium
Many corrosion reactions such as oxidation of metals
Most polymerisation reactions
The Haber-Bosch process of ammonia production
Burning of natural gas
Respiration (endothermic)
Decomposition of vegetable matter into compost

Key points[edit source | edit]

The concept and its opposite number endothermic relate to the enthalpy change in any process, not just chemical reactions.
In endergonic reactions and exergonic reactions it is the sign of the Gibbs free energy that determines the equilibrium point, and not enthalpy. The related concepts endergonic and exergonic apply to all physical processes.
The conceptually related endotherm and exotherm are concepts in animal physiology.
In quantum numbers, when any excited energy level goes down to its original level for example: when n=4 fall to n=2, energy is released so, it is exothermic.
Where an exothermic reaction causes heating of the reaction vessel which is not controlled, the rate of reaction can increase, in turn causing heat to be evolved even more quickly . This positive feedback situation is known as thermal runaway. An explosion can also result from the problem.

Measurement[edit source | edit]

Heat production or absorption in either a physical process or chemical reaction is measured using calorimetry. One common laboratory instrument is the reaction calorimeter, where the heat flow into or from the reaction vessel is monitored. The technique can be used to follow chemical reactions as well as physical processes such as crystallisation and dissolution.

Energy released is measured in Joule per mole. The reaction has a negative ΔH(heat change) value due to heat loss. e.g.: -123 J/mol

References[edit source | edit]

^ Article written by Anne Marie Helmenstine, Ph.D on exothermic and endothermic reactions http://chemistry.about.com/cs/generalchemistry/a/aa051903a.htm
^ Article written by Anne Marie Helmenstine, Ph.D on exothermic and endothermic reactions http://chemistry.about.com/cs/generalchemistry/a/aa051903a.htm
^ http://chemistry.osu.edu/~woodward/ch121/ch5_enthalpy.htm

External links[edit source | edit]

UpToDate Contents

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1. 急性輸血反応が疑われる患者に対するアプローチ approach to the patient with a suspected acute transfusion reaction
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English Journal

Thermal stability and mechanism of decomposition of emulsion explosives in the presence of pyrite.

Xu ZX1, Wang Q1, Fu XQ2.
Journal of hazardous materials.J Hazard Mater.2015 Dec 30;300:702-10. doi: 10.1016/j.jhazmat.2015.07.069. Epub 2015 Aug 4.
The reaction of emulsion explosives (ammonium nitrate) with pyrite was studied using techniques of TG-DTG-DTA. TG-DSC-MS was also used to analyze samples thermal decomposition process. When a mixture of pyrite and emulsion explosives was heated at a constant heating rate of 10K/min from room tempera
PMID 26292057

Reaction between HN and SN: a possible channel for the interstellar formation of N2 and SH in the cold interstellar clouds.

Bhasi P1, Nhlabatsi ZP, Sitha S.
Physical chemistry chemical physics : PCCP.Phys Chem Chem Phys.2015 Dec 28;17(48):32455-63. doi: 10.1039/c5cp05190h. Epub 2015 Nov 23.
Using computational calculations the potential energy surface (PES) of the reaction between NH and NS has been analysed. The PES of the reaction shows the formation of two very stable species, HNSN and HNNS. Out of these two, HNNS which has the signature N-N linkage was found to be the most stable s
PMID 26594029

Thermodynamics and kinetics of inhibitor binding to human equilibrative nucleoside transporter subtype-1.

Rehan S1, Ashok Y1, Nanekar R1, Jaakola VP2.
Biochemical pharmacology.Biochem Pharmacol.2015 Dec 15;98(4):681-9. doi: 10.1016/j.bcp.2015.09.019. Epub 2015 Sep 30.
Many nucleoside transport inhibitors are in clinical use as anti-cancer, vasodilator and cardioprotective drugs. However, little is known about the binding energetics of these inhibitors to nucleoside transporters (NTs) due to their low endogenous expression levels and difficulties in the biophysica
PMID 26428002

Japanese Journal

First-principles simulation of the chemical reactions in GaN growth from Ga

Yamamoto Masahiro,Hamada Noriaki
Jpn. J. Appl. Phys. 53(11), 115601, 2014-10-08
… First-principles calculation has been used to analyze the chemical reaction path in GaN epitaxial crystallization. … The intrinsic reaction coordinates (IRC) have been searched for and the reaction path from Ga<inf>2</inf>O, which is a raw material of GaN, has been clarified. … The reaction path obtained in this work was exothermic as a whole and did not include any fatally large activation barrier. …
NAID 150000109873

Application of remote hydrogen plasma to selective processing for Ge-based devices: Crystallization, etching, and metallization

Makihara Katsunori,Ikeda Mitsuhisa,Okada Tatsuya,Miyazaki Seiichi
Jpn. J. Appl. Phys. 53(11S), 11RA02, 2014-09-30
… After the samples were exposed to the H<inf>2</inf>-RP for 5 min, the crystallization of the whole film was confirmed in Raman scattering spectra, which implies that the exothermic recombination of hydrogen radicals generated in H<inf>2</inf>plasma on a Pt film surface plays an important role in improving the crystallinity caused by energy transfer through the SiO<inf>2</inf>interlayer. …
NAID 150000109858

ポリマーを含有した硝酸アンモニウム/硝酸カリウム微粒子の相安定性および熱分解特性(高エネルギー物質研究会平成25年度研究成果報告書)

永山清一郎,加藤勝美,東英子,中野勝之,羽生宏人
宇宙航空研究開発機構研究開発報告 JAXA-RR-13-009, 23-30, 2014-03
硝酸アンモニウム (AN)は吸湿性を有し,室温近傍においても体積変化を伴う固相間相転移が起こるなど工業利用における課題を有する。我々の既往の研究では,これらの問題を解決するため, AN,相安定化剤である硝酸カリウム (PN)およびポリマー(例:PVA,CMC,Latex)が一体化した微粒子(AN/PN/Polyemer)を調製し,ポリマーの効果により防湿性が向上することを明らかにした。本研究では, …
NAID 110009773561