Term: chemical equilibrium https://doi.org/10.1351/goldbook.C01023 Definition: Reversible processes [processes which may be made to proceed in the forward or reverse direction by the (infinitesimal) change of one variable], ultimately reach a point where the rates in both directions are identical, so that the system gives the appearance of having a static composition at which the Gibbs energy, G, is a minimum. At equilibrium the sum of the chemical potentials of the reactants equals that of the products, so that: \[\Delta G_{\text{r}} = \Delta G_{\text{r}}^{o}+R\ T\ \ln K=0\] \[\Delta G_{\text{r}}^{\,\unicode{x26ac}} = -R\ T\ \ln K\] The equilibrium constant, K, is given by the mass-law effect. Related Terms: 1) variable (http://doi.org/10.1351/goldbook.V06600). 2) equilibrium constant (http://doi.org/10.1351/goldbook.E02177). 3) mass-law effect (http://doi.org/10.1351/goldbook.M03725). Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1114 (https://doi.org/10.1351/pac199466051077) Citation: 'chemical equilibrium' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01023 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.