Editing Exergonic reaction

{{Short description|Chemical reaction that releases more energy than was needed to start it}}
[[File:Exergonic Reaction.svg|thumbnail|An exergonic reaction (such as [[cellular respiration]]) is a reaction that releases free energy in the process of the reaction. The progress of the reaction is shown by the line. [[Activation energy]] (1) slows down the reaction. The change of Gibbs free energy ({{math|Δ''G''}}) in an exergonic reaction (that takes place at constant pressure and temperature) is negative because energy is lost (2).]]

In [[thermochemistry|chemical thermodynamics]], an '''exergonic reaction''' is a [[chemical reaction]] where the change in the [[thermodynamic free energy|free energy]] is negative (there is a net release of free energy).<ref>IUPAC [[Gold Book]] definition: [http://goldbook.iupac.org/terms/view/E02262 exergonic reaction (exoergic reaction)]</ref> This indicates a [[spontaneous reaction]] if the system is [[Closed system|closed]] and initial and final temperatures are the same. For processes that take place in a closed system at constant pressure and temperature, the [[Gibbs free energy]] is used, whereas the [[Helmholtz energy]] is relevant for processes that take place at constant volume and temperature. Any reaction occurring at constant temperature without input of electrical or photon energy is exergonic, according to the [[second law of thermodynamics]]. An example is [[cellular respiration]].

Symbolically, the release of free energy, {{tmath|G}}, in an exergonic reaction (at constant pressure and temperature) is denoted as

:<math>\Delta G=G_{\rm{p}}-G_{\rm{r}}<0.\,</math>

Although exergonic reactions are said to occur ''spontaneously'', this does not imply that the reaction will take place at an observable [[Reaction rate|rate]]. For instance, the [[Catalysis#Example|disproportionation of hydrogen peroxide]] releases free energy but is very slow in the absence of a suitable catalyst. It has been suggested that ''eager'' would be a more intuitive term in this context.<ref>{{cite journal|doi=10.1021/ed061p710|last=Hamori|first=Eugene|author2=James E. Muldrey|year=1984|title=Use of the word "eager" instead of "spontaneous" for the description of exergonic reactions|journal=Journal of Chemical Education|volume=61|issue=8|pages=710|bibcode = 1984JChEd..61..710H }}</ref>

More generally, the terms [[exergonic]] and [[endergonic]] relate to the [[Thermodynamic free energy|free energy]] change in any process, not just chemical reactions. By contrast, the terms [[exothermic]] and [[endothermic]] relate to an [[enthalpy]] change in a closed system during a process, usually associated with the exchange of [[heat]].

==See also==
*[[Endergonic reaction]]

==References==
{{reflist}}

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[[Category:Thermochemistry]]
[[Category:Thermodynamic processes]]