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Exergonic transformations or processes can spontaneously proceed in the forward direction, entailing the irreversible loss of the potential to performe work (erg) with the implication of a positive internal entropy production. Ergodynamic equilibrium is obtained when an exergonic (partial) process is compensated by a coupled endergonic (partial) process, such that the Gibbs energy change of the total transformation is zero. Final thermodynamic equilibrium is reached when all exergonic processes are exhausted and all forces are zero. The backward direction of an exergonic process is endergonic. The distinction between exergonic and exothermic processes is at the heart of ergodynamics, emphasising the concept of exergy changes, linked to the performance of work, in contrast to enthalpy changes, linked to heat or thermal processes, the latter expression being terminologically linked to thermodynamics.

Reference: Gnaiger 1993 Pure Appl Chem

Communicated by Gnaiger E 2018-12-29


Different definitions of the terms exergonic and endergonic derive from the thermodynamics of irreversible processes [1] versus classical thermodynamics with an emphasis on standard Gibbs energy changes [2], in contrast to Gibbs energy changes estimated for actual states.

IUPAC definition

Exergonic (exoergic) reaction: This expression is often applied to a reaction for which the overall standard Gibbs energy change Ξ”GΒ° is negative. Some workers use this term with reference to a negative value of Ξ”HΒ° at the absolute zero of temperature [2].


  1. Gnaiger E (1993) Nonequilibrium thermodynamics of energy transformations. Pure Appl Chem 65:1983-2002. - Β»Bioblast linkΒ«
  2. IUPAC (1997) Compendium of chemical terminology, 2nd ed (the "Gold Book"). Compiled by McNaught AD, Wilkinson A. Blackwell Scientific Publications, Oxford. XML on-line corrected version: http://goldbook.iupac.org (2006-) created by Nic M, Jirat J, Kosata B; updates compiled by Jenkins A. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook. Last update: 2014-02-24; version: 2.3.3.

MitoPedia concepts: Ergodynamics 

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