06171 IUPAC Gold Book - surface excess 10.1351/goldbook.S06171 S06171 current quantity 1 For an interface, the adsorption or surface excess of a given component is defined as the difference between the amount of component actually present in the system, and that which would be present (in a reference system) if the bulk concentration in the adjoining phases were maintained up to a chosen geometrical dividing surface (Gibbs dividing surface). For a solid/liquid interface in which no component of the liquid phase penetrates into the solid, the surface excess (or adsorption) of component i is defined as: \[n_{i}^{\sigma }=n_{i}- V^{\rm{l}}\ c_{i}^{\rm{l}}\] where \(n_{i}\) is the total amount of i in the system, \(V^{\rm{l}}\) is the volume of an arbitrarily chosen amount of bulk liquid (in the framework of the so-called algebraic method) and \(c_{i}^{\rm{l}}\) is its bulk concentration in the liquid. Gibbs adsorption https://goldbook.iupac.org//terms/view/G02627 Gibbs dividing surface https://goldbook.iupac.org//terms/view/G02635 dividing surface https://goldbook.iupac.org//terms/view/D01823 interface https://goldbook.iupac.org//terms/view/I03082 Green Book, 2nd ed., p. 63 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf) PAC, 1986, 58, 967. 'Reporting data on adsorption from solution at the solid/solution interface (Recommendations 1986)' on page 969 (https://doi.org/10.1351/pac198658070967) https://goldbook.iupac.org/terms/view/S06171/html https://goldbook.iupac.org/terms/view/S06171/json https://goldbook.iupac.org/terms/view/S06171/plain Citation: 'surface excess' 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.S06171 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. 2026-06-12T12:03:32+00:00