Endothermic process

File:22. Ендотермна реакција.ogv from ammonium thiocyanate and barium hydroxide is so endothermic that it can freeze a 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.{{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}}

Whether a process can occur spontaneously depends not only on the enthalpy change but also on the entropy change ({{math|∆S}}) and absolute temperature {{mvar|T}}. If a process is a spontaneous process at a certain temperature, the products have a lower Gibbs free energy {{math|1=G = H – TS}} than the reactants (an exergonic process), even if the enthalpy of the products is higher. Thus, an endothermic process usually requires a 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 transitions into more disordered states of higher entropy, e.g. melting and vaporization, are common, spontaneous chemical processes at moderate temperatures are rarely endothermic.{{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}} 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

:C6H12O6 + 6 H2O -> 12 H2 + 6 CO2

:$\backslash Delta\_r\; H^\backslash circ\; =\; +627\; \backslash \; \backslash text\{kJ/mol\},\backslash quad\; \backslash Delta\_r\; G^\backslash circ\; =\; -31\; \backslash \; \backslash text\{kJ/mol\}$.

• Evaporation
• Sublimation
• Cracking of alkanes
• Thermal decomposition
• Hydrolysis
• Nucleosynthesis of elements heavier than nickel in stellar cores{{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}}
• 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 nuclear test produced an unexpectedly high yield.{{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}}
• Nuclear fusion of elements heavier than iron in supernovaeQian, 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}}.
• Dissolving together barium hydroxide and ammonium chloride

The terms "endothermic" and "endotherm" are both derived from 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").{{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}}{{Cite web |title=Meaning of endothermic in English |url=https://dictionary.cambridge.org/dictionary/english/endothermic |website=Cambridge Dictionary |publisher=Cambridge University Press}}

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.{{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}}

{{Reflist}}

• [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