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# Exergonic reaction

An exergonic reaction is a chemical reaction where the variation of Gibbs free energy is negative [1]. This tells us the direction that the reaction will follow. At constant temperature, constant pressure an exergonic reaction is signified by condition:

$\Delta G^\circ < 0$

which describes a chemical reaction that releases energy in the form of heat, light, etc. Exergonic reactions are a form of exergonic processes in general or spontaneous processes and the opposite is called an endergonic reaction. Exergonic reactions are said to occur spontaneously but this does not imply that the reaction will take place unconstrained. For instance the reaction between hydrogen and oxygen is very slow and not observed in absence of a suitable catalyst. It has been suggested to replace the term spontaneous with eager [2].

## Key points

• The concepts exothermic and its opposite number endothermic relate to the enthalpy change in any process not just a chemical reaction.
• the conceptually related endotherm and exotherm are concepts in Animal physiology.

## References

1. ^ IUPAC Gold Book definition Link
2. ^ Use of the world "eager" instead of "spontaneous" for the description of exergonic reactions Hamori, Eugene; Muldrey, James E. Journal of Chemical Education 1984, 61, 710