Editing Exergonic process

{{Short description|Process in which there is a positive flow of energy from the system to the surroundings}}
{{One source|date=May 2009}}
{{Wiktionary|exergonic}}

An '''exergonic process''' is one which there is a positive flow of energy from the system to the surroundings.  This is in contrast with an [[Endergonic reaction|endergonic]] process.<ref>{{GoldBookRef|title=exergonic (exoergic) reaction|file= E02262}}</ref> Constant pressure, constant temperature reactions are exergonic [[if and only if]] the [[Gibbs free energy]] change is negative (∆''G''&nbsp;<&nbsp;0).  "Exergonic" (from the prefix exo-, derived for the Greek word ἔξω ''exō'', "outside" and the suffix -ergonic, derived from the Greek word ἔργον ''ergon'', "[[work (thermodynamics)|work]]") means "releasing energy in the form of work".  In thermodynamics, work is defined as the energy moving from the [[system]] (the internal region) to the [[surroundings]] (the external region) during a given process.

All physical and chemical systems in the universe follow the [[second law of thermodynamics]] and proceed in a downhill, i.e., ''exergonic'', direction.  Thus, left to itself, any physical or chemical system will proceed, according to the [[second law of thermodynamics]], in a direction that tends to lower the [[thermodynamic free energy|free energy]] of the system, and thus to expend energy in the form of work. These reactions occur spontaneously.

A [[chemical reaction]] is also exergonic when spontaneous. Thus in this type of reactions the Gibbs free energy decreases. The [[entropy]] is included in any change of the Gibbs free energy. This differs from an [[exothermic reaction]] or an [[endothermic reaction]] where the entropy is not included. The Gibbs free energy is calculated with the [[Gibbs–Helmholtz equation]]:

: <math>\Delta G = \Delta H- T \cdot \Delta S</math>

where:

: ''T'' = temperature in [[kelvin]]s (K)
: Δ''G'' = change in the Gibbs free energy
: Δ''S'' = change in entropy (at 298 K) as Δ''S'' = Σ<nowiki>{</nowiki>''S''([[Product (chemistry)|Product]])<nowiki>}</nowiki> − Σ<nowiki>{</nowiki>''S''([[Reagent]])<nowiki>}</nowiki>
: Δ''H'' = change in enthalpy (at 298 K) as Δ''H'' = Σ<nowiki>{</nowiki>''H''(Product)<nowiki>}</nowiki> − Σ<nowiki>{</nowiki>''H''(Reagent)<nowiki>}</nowiki>

A chemical reaction progresses spontaneously only when the Gibbs free energy decreases, in that case the Δ''G'' is negative. In exergonic reactions the Δ''G'' is negative and in [[endergonic]] reactions the Δ''G'' is positive:

:<math> \Delta_\mathrm{R} G < 0</math> exergon
:<math> \Delta_\mathrm{R} G > 0</math> endergon

where: 
:<math> \Delta_\mathrm{R} G </math> equals the change in the Gibbs free energy after completion of a chemical reaction.

==See also==
{{div col|colwidth=22em}}
*[[Endergonic]]
*[[Endergonic reaction]]
*[[Exothermic process]]
*[[Endothermic process]]
*[[Exergonic reaction]]
*[[Exothermic reaction]]
*[[Endothermic reaction]]
*[[Warm-blooded|Endotherm]]
*[[Ectotherm]]
{{div col end}}

==References==
{{Reflist}}

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