View source for Endothermic process

{{short description|Thermodynamic process that absorbs energy from its surroundings}}
{{About|the physical effect|self-maintained thermal homeostasis|Endotherm}}An '''endothermic process''' is a chemical or physical process that absorbs heat from its 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> In terms of [[thermodynamics]], it is a [[thermodynamic process]] with an increase in the [[enthalpy]] {{mvar|H}} (or [[internal energy]] {{mvar|U}}) of the system.<ref name="Oxtoby8th">Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015). ''[[iarchive:principlesofmode0000oxto|Principle of Modern Chemistry]]'', Brooks Cole. p. 617.  {{ISBN|978-1305079113}}</ref> In an endothermic process, the heat that a system absorbs is [[thermal energy]] transfer into the system. Thus, an endothermic reaction generally leads to an increase in the [[temperature]] of the system and a decrease in that of the surroundings.<ref name=":0" />

The term was 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 term ''endothermic'' comes from the [[Greek language|Greek]] ἔνδον (''endon'') meaning 'within' and θερμ- (''therm'') meaning 'hot' or 'warm'.<ref>{{Cite web |title=endothermic {{!}} Etymology of endothermic by etymonline |url=https://www.etymonline.com/word/endothermic |access-date=2024-06-28 |website=www.etymonline.com |language=en}}</ref>

An endothermic process may be a chemical process, such as dissolving [[ammonium nitrate]] ({{chem2|NH4NO3}}) in [[water]] ({{chem2|H2O}}), or a physical process, such as the melting of [[ice]] cubes.<ref>{{Citation |last=Lu |first=Jue Xi |title=Biochemistry, Dissolution and Solubility |date=2024 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK431100/ |access-date=2024-06-28 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=28613752 |last2=Tupper |first2=Connor |last3=Gutierrez |first3=Alejandra V. |last4=Murray |first4=John}}</ref>

The opposite of an endothermic process is an [[exothermic process]], one that releases or "gives out" energy, usually in the form of heat and sometimes as [[electrical energy]].<ref name=":0" /> Thus, ''endo'' in endothermic refers to energy or heat going in, and ''exo'' in exothermic refers to energy or heat going out. In each term (endothermic and exothermic) the prefix refers to where heat (or electrical energy) goes as the process occurs.<ref>{{Cite web |title=Endothermic & Exothermic Reactions |url=https://www.ashrae.org/file%20library/communities/student%20zone/k-12%20activities/ashrae-endothermic---exothermic-reactions-stem-kit.pdf |access-date=2024-06-28 |website=Ashrae}}</ref>

==In chemistry==
[[File:22. Ендотермна реакција.ogv|thumb|right|The formation of [[barium thiocyanate]] from [[ammonium thiocyanate]] and [[barium hydroxide]] is so endothermic that it can freeze a [[beaker (lab equipment)|beaker]] to wet [[styrofoam]]]]
Due to bonds breaking and forming during various processes (changes in state, chemical reactions), there is usually a change in energy. If the energy of the forming bonds is greater than the energy of the breaking bonds, then energy is released. This is known as an exothermic reaction. However, if more energy is needed to break the bonds than the energy being released, energy is taken up. Therefore, it is an '''endothermic reaction'''.<ref>{{Cite web |title=Exothermic & Endothermic Reactions |url=https://highschoolenergy.acs.org/content/hsef/en/how-can-energy-change/exothermic-endothermic.html |access-date=2021-04-11 |website=Energy Foundations for High School Chemistry |publisher=American Chemical Society}}</ref>

==Details==
Whether a process can occur spontaneously depends not only on the [[enthalpy]] change but also on the [[entropy]] change ({{math|∆''S''}}) and [[Thermodynamic temperature|absolute temperature]] {{mvar|T}}. If a process is a [[spontaneous process]] at a certain temperature, the products have a lower [[Thermodynamic free energy|Gibbs free energy]] {{math|1=''G'' = ''H'' – ''TS''}} than the reactants (an [[exergonic process]]),<ref name="Oxtoby8th"/> even if the enthalpy of the products is higher. Thus, an endothermic process usually requires a [[Entropy production|favorable entropy increase]] ({{math|∆''S'' > 0}}) in the system that overcomes the unfavorable increase in enthalpy so that still {{math|∆''G'' < 0}}. While endothermic [[phase transition]]s into more disordered states of higher entropy, e.g. melting and vaporization, are common, spontaneous chemical processes at moderate temperatures are rarely endothermic.<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=2024-06-28 |website=www.chemicool.com}}</ref> The enthalpy increase{{math| ∆''H'' ≫ 0}} in a hypothetical strongly endothermic process usually results in {{math|1=∆''G'' = ∆''H'' – ''T''∆''S'' > 0}}, which means that the process will not occur (unless driven by electrical or photon energy). An example of an endothermic and exergonic process is

:<chem>C6H12O6 + 6 H2O -> 12 H2 + 6 CO2</chem>
:<math>\Delta_r H^\circ = +627 \ \text{kJ/mol},\quad  \Delta_r G^\circ = -31 \ \text{kJ/mol}</math>.

==Examples==
* [[Evaporation]]
* [[Sublimation (phase transition)|Sublimation]]
* [[Cracking (chemistry)|Cracking]] of [[alkane]]s
* [[Thermal decomposition]]
* [[Hydrolysis]]
* [[Nucleosynthesis]] of elements heavier than [[nickel]] in stellar cores<ref>{{Cite web |last= |date=2017-05-15 |title=Galactic nucleosynthesis: the onset of element production in our galaxy |url=https://researchfeatures.com/galactic-nucleosynthesis/ |access-date=2024-06-28 |website=Research Features |language=en-GB}}</ref>
* High-energy neutrons can produce [[tritium]] from [[lithium-7]] in an endothermic process, consuming 2.466 [[MeV]]. This was discovered when the 1954 [[Castle Bravo#High yield|Castle Bravo]] nuclear test produced an unexpectedly high yield.<ref name="ieer">{{Cite web|url=http://www.ieer.org/reports/tritium.html#(11)|title=Tritium: The environmental, health, budgetary, and strategic effects of the Department of Energy's decision to produce tritium|last=Austin|first=Patrick|date=January 1996|publisher=[[Institute for Energy and Environmental Research]]|access-date=2010-09-15}}</ref>
* [[Nuclear fusion]] of elements heavier than [[iron]] in [[supernova]]e<ref>Qian, Y.-Z.; Vogel, P.; Wasserburg, G. J. (1998). "Diverse Supernova Sources for the r-Process". Astrophysical Journal 494 (1): 285–296. {{arxiv|astro-ph/9706120}}. {{Bibcode|1998ApJ...494..285Q}}. {{doi|10.1086/305198}}.</ref>
* Dissolving together [[barium hydroxide]] and [[ammonium chloride]]

==Distinction between endothermic and endotherm==
The terms "endothermic" and "endotherm" are both derived from [[Ancient Greek|Greek]] {{Lang|grc|ἔνδον|italic=no}} ''{{Lang|grc-latn|endon}}'' "within" and {{Lang|grc|θέρμη|italic=no}} ''{{Lang|grc-latn|thermē}}'' "heat", but depending on context, they can have very different meanings.

In physics, [[thermodynamics]] applies to processes involving a system and its surroundings, and the term "endothermic" is used to describe a reaction where energy is taken "(with)in" by the system (vs. an "exothermic" reaction, which releases energy "outwards").<ref>{{Cite web |date=2014-11-18 |title=5.2: The First Law of Thermodynamics |url=https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-_The_Central_Science_(Brown_et_al.)/05%3A_Thermochemistry/5.02%3A_The_First_Law_of_Thermodynamics |access-date=2024-06-28 |website=Chemistry LibreTexts |language=en}}</ref><ref>{{Cite web |title=Meaning of endothermic in English |url=https://dictionary.cambridge.org/dictionary/english/endothermic |website=Cambridge Dictionary |publisher=Cambridge University Press}}</ref>

In biology, [[thermoregulation]] is the ability of an [[organism]] to maintain its body temperature, and the term "[[endotherm]]" refers to an organism that can do so from "within" by using the heat released by its internal bodily functions (vs. an "[[ectotherm]]", which relies on external, environmental heat sources) to maintain an adequate temperature.<ref>{{Cite web |title=Endotherm {{!}} Homeothermy, Thermoregulation, Metabolism {{!}} Britannica |url=https://www.britannica.com/science/endotherm |access-date=2024-06-28 |website=www.britannica.com |language=en}}</ref>

==References==
{{Reflist}}

==External links==
* [http://www.ilpi.com/msds/ref/exothermic.html Exothermic and Endothermic] – MSDS Hyper-Glossary at Interactive Learning Paradigms, Incorporated

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[[Category:Thermochemistry]]
[[Category:Thermodynamic processes]]
[[Category:Chemical thermodynamics]]