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Explosions are some of the most violent exothermic reactions.

In thermodynamics, an exothermic process (from Ancient Greek έξω (éxō) 'outward' and θερμικός (thermikós) 'thermal')^[1] is a thermodynamic process or reaction that releases energy from the system to its surroundings,^[2] usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e.g. a battery), or sound (e.g. explosion heard when burning hydrogen). The term exothermic was first coined by 19th-century French chemist Marcellin Berthelot.^[3]

The opposite of an exothermic process is an endothermic process, one that absorbs energy, usually in the form of heat.^[2] The concept is frequently applied in the physical sciences to chemical reactions where chemical bond energy is converted to thermal energy (heat).

Two types of chemical reactions

Exothermic and endothermic describe two types of chemical reactions or systems found in nature, as follows:

Exothermic

An exothermic reaction occurs when heat is released to the surroundings. According to the IUPAC, an exothermic reaction is "a reaction for which the overall standard enthalpy change ΔH⚬ is negative".^[4] Some examples of exothermic process are fuel combustion, condensation and nuclear fission,^[5] which is used in nuclear power plants to release large amounts of energy.^[6]

Endothermic

In an endothermic reaction or system, energy is taken from the surroundings in the course of the reaction, usually driven by a favorable entropy increase in the system.^[7] An example of an endothermic reaction is a first aid cold pack, in which the reaction of two chemicals, or dissolving of one in another, requires calories from the surroundings, and the reaction cools the pouch and surroundings by absorbing heat from them.^[8]

Photosynthesis, the process that allows plants to convert carbon dioxide and water to sugar and oxygen, is an endothermic process: plants absorb radiant energy from the sun and use it in an endothermic, otherwise non-spontaneous process. The chemical energy stored can be freed by the inverse (spontaneous) process: combustion of sugar, which gives carbon dioxide, water and heat (radiant energy).^[9]

Energy release

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.

\Delta H<0,

^[10]

while at constant volume, according to the first law of thermodynamics it equals internal energy ( $U$ ) change, i.e.

\Delta U=Q+0>0.

In an adiabatic system (i.e. a system that does not exchange heat with the surroundings), an otherwise exothermic process results in an increase in temperature of the system.^[11]

In exothermic chemical reactions, the heat that is released by the reaction takes the form of electromagnetic energy or kinetic energy of molecules.^[12] The transition of electrons from one quantum energy level to another causes light to be released. This light is equivalent in energy to some of the stabilization energy of the energy for the chemical reaction, i.e. the bond energy. 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 activation energy (energy needed to start the reaction) is less than the energy that is subsequently released, so there is a net release of energy.^[13]

Examples

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

Some examples of exothermic processes are:^[14]

Combustion of fuels such as wood, coal and oil/petroleum
The thermite reaction^[15]
The reaction of alkali metals and other highly electropositive metals with water
Condensation of rain from water vapor
Mixing water and strong acids or strong bases
The reaction of acids and bases
Dehydration of carbohydrates by sulfuric acid
The setting of cement and concrete
Some polymerization reactions such as the setting of epoxy resin
The reaction of most metals with halogens or oxygen
Nuclear fusion in hydrogen bombs and in stellar cores (to iron)
Nuclear fission of heavy elements
The reaction between zinc and hydrochloric acid
Respiration (breaking down of glucose to release energy in cells)

Implications for chemical reactions

Chemical exothermic reactions are generally more spontaneous than their counterparts, endothermic reactions.^[16]

In a thermochemical reaction that is exothermic, the heat may be listed among the products of the reaction.

References

^ "Gate for the Greek language" on-line dictionary Archived 2017-12-05 at the Wayback Machine. greek-language.gr
^ ^a ^b "17.3: Exothermic and Endothermic Processes". Chemistry LibreTexts. 2016-06-27. Retrieved 2024-06-26.
^ Sutton, Mike (2007-03-01). "Chemistry for the common good". Chemistry World. Retrieved 2024-06-26.
^ "IUPAC - exothermic reaction (E02269)". goldbook.iupac.org. The International Union of Pure and Applied Chemistry (IUPAC). doi:10.1351/goldbook.e02269. Retrieved 2024-06-26.
^ Bashyal, Jyoti (2023-02-20). "Exothermic reactions with Important Examples". scienceinfo.com. Retrieved 2024-06-26.
^ "Nuclear power plants - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2024-06-26.
^ Oxtoby, David W.; Gillis, H. P.; Butler, Laurie J. (2016). Principles of modern chemistry (8 ed.). Andover: Cengage Learning. p. 617. ISBN 978-1-305-07911-3.
^ "The Cold Pack: A Chilly Example of an Endothermic Reaction - Let's Talk Science". letstalkscience.ca. 2020-06-01. Retrieved 2024-06-26.
^ "Photosynthesis - What happens during photosynthesis? - OCR 21st Century - GCSE Combined Science Revision - OCR 21st Century". BBC Bitesize. Retrieved 2024-06-26.
^ Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).Principles of Modern Chemistry, Brooks Cole. p. 617. ISBN 978-1305079113
^ Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. pp. 6–7. ISBN 0-19-856552-6.
^ "Potential Energy". Chemistry LibreTexts. 2013-10-02. Retrieved 2024-06-26.
^ "Chapter 2 - Carbon-based fuels". Heinemann Chemistry. Vol. 2 (6 ed.). Pearson. pp. 64–65. ISBN 9780655700098.
^ Exothermic – Endothermic examples Archived 2006-09-01 at the Wayback Machine. frostburg.edu
^ "T510: Exothermic Reaction – Thermite". 23 December 2015.
^ "Examples of Spontaneous Endothermic Reactions - Chemistry Examples". www.chemicool.com. Retrieved 2024-06-26.

External links

Observe exothermic reactions in a simple experiment Archived 2006-05-22 at the Wayback Machine

[1] "Gate for the Greek language" on-line dictionary Archived 2017-12-05 at the Wayback Machine. greek-language.gr

[:0-2] "17.3: Exothermic and Endothermic Processes". Chemistry LibreTexts. 2016-06-27. Retrieved 2024-06-26.

[3] Sutton, Mike (2007-03-01). "Chemistry for the common good". Chemistry World. Retrieved 2024-06-26.

[4] "IUPAC - exothermic reaction (E02269)". goldbook.iupac.org. The International Union of Pure and Applied Chemistry (IUPAC). doi:10.1351/goldbook.e02269. Retrieved 2024-06-26.

[5] Bashyal, Jyoti (2023-02-20). "Exothermic reactions with Important Examples". scienceinfo.com. Retrieved 2024-06-26.

[6] "Nuclear power plants - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2024-06-26.

[7] Oxtoby, David W.; Gillis, H. P.; Butler, Laurie J. (2016). Principles of modern chemistry (8 ed.). Andover: Cengage Learning. p. 617. ISBN 978-1-305-07911-3.

[8] "The Cold Pack: A Chilly Example of an Endothermic Reaction - Let's Talk Science". letstalkscience.ca. 2020-06-01. Retrieved 2024-06-26.

[9] "Photosynthesis - What happens during photosynthesis? - OCR 21st Century - GCSE Combined Science Revision - OCR 21st Century". BBC Bitesize. Retrieved 2024-06-26.

[Oxtoby8th-10] Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).Principles of Modern Chemistry, Brooks Cole. p. 617. ISBN 978-1305079113

[11] Perrot, Pierre (1998). A to Z of Thermodynamics. Oxford University Press. pp. 6–7. ISBN 0-19-856552-6.

[12] "Potential Energy". Chemistry LibreTexts. 2013-10-02. Retrieved 2024-06-26.

[13] "Chapter 2 - Carbon-based fuels". Heinemann Chemistry. Vol. 2 (6 ed.). Pearson. pp. 64–65. ISBN 9780655700098.

[14] Exothermic – Endothermic examples Archived 2006-09-01 at the Wayback Machine. frostburg.edu

[15] "T510: Exothermic Reaction – Thermite". 23 December 2015.

[16] "Examples of Spontaneous Endothermic Reactions - Chemistry Examples". www.chemicool.com. Retrieved 2024-06-26.

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+{{short description|Thermodynamic process that releases energy to its surroundings}}
-In [[thermodynamics]], the  word '''exothermic''' describes a process or reaction that releases [[energy]] in the form of [[heat]].  Its etymology stems from the Greek prefix ''ex-,'' meaning “outside” and the Greek word ''thermein'', meaning “to heat”.  The term “exothermic” was coined by [[Marcellin Berthelot]].  The opposite of an exothermic process is an [[endothermic]] process, one that absorbs energy in the form of heat.
+{{Distinguish|Ectothermic}}
+[[File:Explosion1.JPG|thumb|right|300px|[[Explosion]]s are some of the most violent exothermic reactions.]]
+In [[thermodynamics]], an '''exothermic process''' ({{etymology|grc|''{{Wikt-lang|grc|έξω}}'' ({{grc-transl|έξω}})|outward||''{{Wikt-lang|grc|θερμικός}}'' ({{grc-transl|θερμικός}})|thermal}})<ref>[http://www.greek-language.gr/greekLang/modern_greek/tools/lexica/search.html?lq=%CE%B8%CE%B5%CF%81%CE%BC%CE%B9%CE%BA%CF%8C%CF%82&dq= "Gate for the Greek language" on-line dictionary] {{webarchive|url=https://web.archive.org/web/20171205235500/http://www.greek-language.gr/greekLang/modern_greek/tools/lexica/search.html?lq=%CE%B8%CE%B5%CF%81%CE%BC%CE%B9%CE%BA%CF%8C%CF%82&dq= |date=2017-12-05 }}. greek-language.gr</ref> is a [[thermodynamic process]] or [[chemical reaction|reaction]] that releases [[energy]] from the system to its [[environment (systems)|surroundings]],<ref name=":0">{{Cite web |date=2016-06-27 |title=17.3: Exothermic and Endothermic Processes |url=https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introductory_Chemistry_(CK-12)/17%3A_Thermochemistry/17.03%3A_Exothermic_and_Endothermic_Processes |access-date=2024-06-26 |website=Chemistry LibreTexts |language=en}}</ref> usually in the form of [[heat]], but also in a form of [[light]] (e.g. a spark, flame, or flash), [[electricity]] (e.g. a battery), or [[sound]] (e.g. explosion heard when burning hydrogen). The term ''exothermic'' was first coined by 19th-century French chemist [[Marcellin Berthelot]].<ref>{{Cite web |last=Sutton |first=Mike |date=2007-03-01 |title=Chemistry for the common good |url=https://www.chemistryworld.com/features/chemistry-for-the-common-good/3004535.article |access-date=2024-06-26 |website=Chemistry World |language=en}}</ref>
-The concept is frequently applied in [[physical sciences]] to e.g. [[chemical reactions]], where chemical [[bond energy]] is converted to [[thermal energy]] (heat).
+The opposite of an exothermic process is an [[endothermic]] process, one that absorbs energy, usually in the form of heat.<ref name=":0" />  The concept is frequently applied in the [[Outline of physical science|physical sciences]] to [[chemical reaction]]s where chemical [[bond energy]] is converted to [[thermal energy]] (heat).
-==Overview==
-Exothermic refers to a transformation in which a system releases energy (heat) to the surroundings:
+==Two types of chemical reactions==
-:Q < 0
+Exothermic and endothermic describe two types of chemical reactions or systems found in nature, as follows:
+=== Exothermic===
-When the transformation occurs at constant pressure:
+An exothermic reaction occurs when heat is released to the surroundings. According to the [[International Union of Pure and Applied Chemistry|IUPAC]], an exothermic reaction is "a reaction for which the overall standard [[enthalpy]] change Δ''H''⚬ is negative".<ref>{{Cite web |last= |first= |title=IUPAC - exothermic reaction (E02269) |url=https://goldbook.iupac.org/terms/view/E02269 |access-date=2024-06-26 |website=goldbook.iupac.org |publisher=The International Union of Pure and Applied Chemistry (IUPAC) |doi=10.1351/goldbook.e02269}}</ref> Some examples of exothermic process are fuel [[combustion]], [[condensation]] and [[nuclear fission]],<ref>{{Cite web |last=Bashyal |first=Jyoti |date=2023-02-20 |title=Exothermic reactions with Important Examples |url=https://scienceinfo.com/exothermic-reactions-with-important-examples/ |access-date=2024-06-26 |website=scienceinfo.com |language=en-US}}</ref> which is used in [[nuclear power plant]]s to release large amounts of energy.<ref>{{Cite web |title=Nuclear power plants - U.S. Energy Information Administration (EIA) |url=https://www.eia.gov/energyexplained/nuclear/nuclear-power-plants.php |access-date=2024-06-26 |website=www.eia.gov}}</ref>
+===Endothermic===
-:''∆H < 0''
+In an [[Endothermic process|endothermic reaction]] or system, energy is taken from the surroundings in the course of the reaction, usually driven by a favorable [[entropy]] increase in the system.<ref>{{Cite book |last=Oxtoby |first=David W. |title=Principles of modern chemistry |last2=Gillis |first2=H. P. |last3=Butler |first3=Laurie J. |date=2016 |publisher=Cengage Learning |isbn=978-1-305-07911-3 |edition=8 |location=Andover |pages=617}}</ref> An example of an endothermic reaction is a first aid cold pack, in which the reaction of two chemicals, or dissolving of one in another, requires calories from the surroundings, and the reaction cools the pouch and surroundings by absorbing heat from them.<ref>{{Cite web |date=2020-06-01 |title=The Cold Pack: A Chilly Example of an Endothermic Reaction - Let's Talk Science |url=https://letstalkscience.ca/educational-resources/stem-in-context/cold-pack-a-chilly-example-endothermic-reaction |access-date=2024-06-26 |website=letstalkscience.ca |language=en}}</ref>
+[[Photosynthesis]], the process that allows plants to convert carbon dioxide and water to sugar and oxygen, is an endothermic process: plants absorb [[radiant energy]] from the sun and use it in an endothermic, otherwise non-spontaneous process. The chemical energy stored can be freed by the inverse (spontaneous) process: combustion of sugar, which gives carbon dioxide, water and heat (radiant energy).<ref>{{Cite web |title=Photosynthesis - What happens during photosynthesis? - OCR 21st Century - GCSE Combined Science Revision - OCR 21st Century |url=https://www.bbc.co.uk/bitesize/guides/z9pjrwx/revision/1 |access-date=2024-06-26 |website=BBC Bitesize |language=en-GB}}</ref>
-and constant volume:
+==Energy release==
-:''∆U < 0''
+Exothermic refers to a transformation in which a closed system releases energy (heat) to the surroundings, expressed by
+:<math>Q > 0.</math>
-YOUR ALL GAY HAHA
+When the transformation occurs at [[Isobaric process|constant pressure]] and without exchange of [[electrical energy]], heat {{mvar|Q}} is equal to the [[enthalpy]] change, i.e.
-In an [[adiabatic]] system (i.e. a system that does not give off heat to the surroundings), an exothermic process results in an increase in temperature.<ref>{{cite book | last = Perrot | first = Pierre | title = A to Z of Thermodynamics | publisher = Oxford University Press | year = 1998 | id = ISBN 0-19-856552-6 }}</ref>
+:<math>\Delta H < 0,</math><ref name="Oxtoby8th">Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principles of Modern Chemistry'', Brooks Cole. p. 617.  {{ISBN|978-1305079113}}</ref>
-===Exothermic processes===
-Some examples of exothermic processes are:<ref>[http://antoine.frostburg.edu/chem/senese/101/thermo/faq/exothermic-endothermic-examples.shtml Exothermic - Endothermic examples]</ref>
+while at [[constant volume]], according to the [[first law of thermodynamics]] it equals [[internal energy]] ({{mvar|U}}) change, i.e.
-* Condensation of rain from water vapor
-* Combustion (for instance of a candle)
+:<math>\Delta U = Q + 0 > 0.</math>
-* Mixing water and strong acids
-* Nuclear fusion
+In an [[adiabatic]] system (i.e. a system that does not exchange heat with the surroundings), an otherwise exothermic process results in an increase in temperature of the system.<ref>{{cite book |last=Perrot |first=Pierre |title=A to Z of Thermodynamics |publisher=Oxford University Press |year=1998 |isbn=0-19-856552-6 |pages=6–7}}</ref>
+In exothermic chemical reactions, the heat that is released by the reaction takes the form of electromagnetic energy or [[kinetic energy]] of molecules.<ref>{{Cite web |date=2013-10-02 |title=Potential Energy |url=https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Thermodynamics/Energies_and_Potentials/Potential_Energy |access-date=2024-06-26 |website=Chemistry LibreTexts |language=en}}</ref> The transition of [[electron]]s from one quantum [[energy level]] to another causes light to be released. This light is equivalent in energy to some of the stabilization energy of the energy for the chemical reaction, i.e. the [[bond energy]]. This light that is released can be absorbed by other molecules in [[Solution (chemistry)|solution]] to give rise to molecular translations and rotations, which gives rise to the classical understanding of heat. In an exothermic reaction, the [[activation energy]] (energy needed to start the reaction) is less than the energy that is subsequently released, so there is a net release of energy.<ref>{{Cite book |title=Heinemann Chemistry |publisher=[[Pearson Education|Pearson]] |isbn=9780655700098 |edition=6 |volume=2 |pages=64–65 |language=en |chapter=Chapter 2 - Carbon-based fuels}}</ref>
+==Examples==
+[[Image:ThermiteReaction.jpg|thumb|right|An exothermic [[thermite]] reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.]]
+Some examples of exothermic processes are:<ref>[http://antoine.frostburg.edu/chem/senese/101/thermo/faq/exothermic-endothermic-examples.shtml Exothermic – Endothermic examples] {{webarchive|url=https://web.archive.org/web/20060901100540/http://antoine.frostburg.edu/chem/senese/101/thermo/faq/exothermic-endothermic-examples.shtml |date=2006-09-01 }}. frostburg.edu</ref>
+* [[Combustion]] of [[fuel]]s such as [[wood]], [[coal]] and [[oil]]/[[petroleum]]
+* The thermite reaction<ref>{{cite web | url=https://www.colorado.edu/lab/lecture-demo-manual/t510-exothermic-reaction-thermite | title=T510: Exothermic Reaction – Thermite | date=23 December 2015 }}</ref>
+* The reaction of [[alkali metal]]s and other highly [[electropositive]] metals with water
+* [[Condensation]] of rain from water vapor
+* Mixing water and [[strong acid]]s or [[strong base]]s
+* The reaction of [[acid]]s and [[base (chemistry)|bases]]
+* Dehydration of [[carbohydrate]]s by [[sulfuric acid]]
+* The setting of [[cement]] and [[concrete]]
+* Some [[polymerisation|polymerization]] reactions such as the setting of [[epoxy resin]]
+* The reaction of most metals with halogens or oxygen
+* [[Nuclear fusion]] in hydrogen bombs and in stellar cores (to iron)
+* [[Nuclear fission]] of heavy elements
+* The reaction between zinc and [[hydrochloric acid]]
+* [[Cellular respiration|Respiration]] (breaking down of glucose to release energy in cells)
 ==Implications for chemical reactions==
-{{main|exothermic reaction}}
+{{main|Exothermic reaction}}
-Chemical exothermic reactions are generally more spontaneous than their counterparts, [[endothermic reaction]]s.  In a thermochemical reaction that is exothermic, the heat is placed as a product on the product's side (heat is a product of the reaction).
+Chemical exothermic reactions are generally more spontaneous than their counterparts, [[endothermic reaction]]s.<ref>{{Cite web |title=Examples of Spontaneous Endothermic Reactions - Chemistry Examples |url=https://www.chemicool.com/examples/spontaneous-endothermic-reactions.html#:~:text=Hence%20reactions%20are%20spontaneous%20only,in%20free%20energy,%20is%20negative.&text=Exothermic%20reactions%20have%20negative%20values,with%20positive%20values%20of%20%CE%94H. |access-date=2024-06-26 |website=www.chemicool.com}}</ref>
+In a thermochemical reaction that is exothermic, the heat may be listed among the products of the reaction.
 ==See also==
+{{div col|colwidth=22em}}
-{{wiktionary|exothermic}}
+* [[Calorimetry]]
+* [[Chemical thermodynamics]]
+* [[Differential scanning calorimetry]]
 * [[Endergonic]]
 * [[Endergonic reaction]]
 * [[Exergonic]]
 * [[Exergonic reaction]]
+* [[Endothermic reaction]]
+{{div col end}}
+==References==
+{{reflist}}
 ==External links==
+{{wiktionary|exothermic}}
-* http://chemistry.about.com/b/a/184556.htm Observe exothermic reactions in a simple experiment
+* [http://chemistry.about.com/b/a/184556.htm Observe exothermic reactions in a simple experiment] {{Webarchive|url=https://web.archive.org/web/20060522175716/http://chemistry.about.com/b/a/184556.htm |date=2006-05-22 }}
-[[Category:Thermodynamics]]
+[[Category:Thermodynamic processes]]
-==References==
+[[Category:Chemical thermodynamics]]
-<references />
-[[ar:تفاعل طارد للحرارة]]
-[[ca:Reacció exotèrmica]]
 [[da:Exoterm]]
-[[de:exotherm]]
-[[es:Reacción exotérmica]]
-[[et:Eksotermiline reaktsioon]]
-[[fr:Réaction exothermique]]
-[[he:תגובה אקסותרמית]]
-[[hu:Exoterm reakció]]
-[[it:Processo esotermico]]
-[[lt:Egzoterminis procesas]]
-[[mk:Егзотермна реакција]]
-[[nl:exotherm]]
-[[nn:Eksoterm reaksjon]]
-[[sk:Exotermická reakcia]]
-[[fi:Eksoterminen reaktio]]
-[[sv:Exoterm]]
-[[tr:Ekzotermik]]
-[[zh:放热反应]]