View source for Exothermic process

{{short description|Thermodynamic process that releases energy to its surroundings}}
{{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 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).
==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 [[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===
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>
==Energy release==
Exothermic refers to a transformation in which a closed system releases energy (heat) to the surroundings, expressed by
:<math>Q > 0.</math>
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.
:<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>
while at [[constant volume]], according to the [[first law of thermodynamics]] it equals [[internal energy]] ({{mvar|U}}) change, i.e.
:<math>\Delta U = Q + 0 > 0.</math>
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}}
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}}
* [[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] {{Webarchive|url=https://web.archive.org/web/20060522175716/http://chemistry.about.com/b/a/184556.htm |date=2006-05-22 }}
[[Category:Thermodynamic processes]]
[[Category:Chemical thermodynamics]]
[[da:Exoterm]]