06442 IUPAC Gold Book - transfer activity coefficient 10.1351/goldbook.T06442 T06442 current 1 A term used to quantify the difference in the free energy of a solute ion in two different standard states often in two different liquid phases. The relationship is \(\Delta _{\rm{t}}G^{\,\unicode{x26ac}} = \nu \ R\ T\ \ln \mathit{\gamma}_{\rm{t}}\) where \(\Delta _{\rm{t}}G^{\,\unicode{x26ac}}\) is the transfer Gibbs energy and \(\nu \) is the number of ions in the solute. It should not be confused with the mass transfer coefficient which represents the specific rate of transfer of a species from one phase to another. It does not necessarily imply the physical transfer of a solute between two liquid phases. coefficient https://goldbook.iupac.org//terms/view/C01124 free energy https://goldbook.iupac.org//terms/view/F02515 partition constant https://goldbook.iupac.org//terms/view/P04438 PAC, 1993, 65, 2373. 'Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations 1993)' on page 2386 (https://doi.org/10.1351/pac199365112373) https://goldbook.iupac.org/terms/view/T06442/html https://goldbook.iupac.org/terms/view/T06442/json https://goldbook.iupac.org/terms/view/T06442/plain Citation: 'transfer activity coefficient' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.T06442 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. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . 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. 2026-07-28T13:35:46+00:00