Title: surface excess isotherm
Long Title: IUPAC Gold Book - surface excess isotherm
DOI: 10.1351/goldbook.S06178
Status: current

Definition
The function relating, at constant temperature and pressure, \(\mathit{\Gamma}_{i}^{\left(\rm{n}\right)}\), \(\mathit{\Gamma}_{i}^{\left(\rm{l}\right)}\) or \(\mathit{\Gamma}_{i}^{\left(\rm{v}\right)}\), or the respective specific quantities \(\frac{n^{\rm{l}}\ \Delta x_{i}^{\rm{l}}}{m}\), \(\frac{A_{\rm{s}}\ \mathit{\Gamma }_{i}^{\left(\rm{l}\right)}}{m}\) or \(\frac{V^{\rm{l}}\ \Delta c_{i}^{\rm{l}}}{m}\) to the mole fraction (or concentration) of component \(i\) in the equilibrium liquid phase. With solutions of more than two components such isotherms are unequivocal functions only when the ratios of the mole fractions (or concentrations) of all other components except \(i\) are kept constant. (\(A_{\rm{s}}\) is the area of interface, \(\mathit{\Gamma}_{i}^{\left(\rm{n}\right)}\), \(\mathit{\Gamma}_{i}^{\left(\rm{l}\right)}\), \(\mathit{\Gamma}_{i}^{\left(\rm{v}\right)}\) are relative adsorptions, \(\Delta x_{i}^{\rm{l}}\) is the change in mole fraction of \(i\) resulting from bringing a specified mass \(m\) of solid into contact with a specified amount of solution \(n^{\rm{l}}\), \(\Delta c_{i}^{\rm{l}}\) is the change in concentration resulting from bringing a specified mass of solid into contact with a specified amount of solution of volume \(V^{\rm{l}}\).)

Related Terms
- area of interface: https://goldbook.iupac.org//terms/view/A00430
- mole: https://goldbook.iupac.org//terms/view/M03980
- mole fraction: https://goldbook.iupac.org//terms/view/A00296

Source
- PAC, 1972, 31, 577. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry' on page 593 (https://doi.org/10.1351/pac197231040577)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/S06178/html
- json: https://goldbook.iupac.org/terms/view/S06178/json
- xml: https://goldbook.iupac.org/terms/view/S06178/xml

Citation: Citation: 'surface excess isotherm' 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.S06178
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.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
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.
Accessed: 2025-11-19T01:26:25+00:00