{"term":{"id":"03577","title":"Lippman's equation","longtitle":"IUPAC Gold Book - Lippman's equation","doi":"10.1351\/goldbook.L03577","code":"L03577","status":"current","definitions":[{"id":1,"text":"An equation which gives the electric charge per unit area of an interface (electrode): \\[(\\frac{\\partial \\gamma }{\\partial E_{\\rm{A}}})_{T,p,\\mu _{i}\\neq \\mu }=- Q_{\\rm{A}}\\] where \\(\\gamma \\) is the interfacial tension, \\(E_{\\rm{A}}\\) is the potential of a cell in which the reference electrode has an interfacial equilibrium with one of the ionic components of A, \\(Q_{\\rm{A}}\\) is the charge on unit area of the interface, \\(\\mu _{i}\\) is the chemical potential of the combination of species \\(i\\) whose net charge is zero, \\(T\\) is the thermodynamic temperature and \\(p\\) is the external pressure. Since more than one type of reference electrode may be chosen, more than one quantity \\(Q\\) may be obtained. Consequently \\(Q\\) cannot be considered as equivalent to the physical charge on a particular region of the interphase. It is in fact an alternative way of expressing a surface excess or combination of surface excess of charged species.","links":[{"term":"chemical potential","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/C01032"},{"term":"electric charge","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/E01923"},{"term":"interface","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/I03082"},{"term":"interfacial tension","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/I03088"},{"term":"interphase","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/I03118"},{"term":"reference electrode","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/R05229"},{"term":"surface excess","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/S06171"},{"term":"thermodynamic temperature","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/T06321"}],"sources":["PAC, 1974, 37, 499. 'Electrochemical nomenclature' on page 508 (https:\/\/doi.org\/10.1351\/pac197437040499)","PAC, 1986, 58, 437. 'Interphases in systems of conducting phases (Recommendations 1985)' on page 445 (https:\/\/doi.org\/10.1351\/pac198658030437)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/L03577\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/L03577\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/L03577\/plain"},"citation":"Citation: 'Lippman's equation' 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.L03577","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":"2026-06-28T16:39:04+00:00"}}