Term: mass-law effect
https://doi.org/10.1351/goldbook.M03725

Definition:
At equilibrium, the product of the activities (or concentrations) of the reacting species is constant. Thus for the equilibrium: \[\alpha\,\text{A}\,+\,\beta\,\text{B}\rightleftharpoons \gamma\,\text{C}\,+\,\delta\,\text{D}\] \[K=\frac{\left[\text{C}\right]^{\gamma }\ \left[\text{D}\right]^{\delta }}{\left[\text{A}\right]^{\alpha }\ \left[\text{B}\right]^{\beta }}\]

Related Terms:
1) common-ion effect (http://doi.org/10.1351/goldbook.C01191).
2) equilibrium (http://doi.org/10.1351/goldbook.C01023).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1138 (https://doi.org/10.1351/pac199466051077)

Citation: 'mass-law effect' 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.M03725

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