{"term":{"id":"09068","title":"Nernst equation","longtitle":"IUPAC Gold Book - Nernst equation","doi":"10.1351\/goldbook.09068","code":"09068","status":"current","definitions":[{"id":1,"text":"Fundamental equation in electrochemistry that describes the dependence of the equilibrium electrode potential on the composition of the contacting phases, written as a reduction: \\[E_{\\rm{eq}} = E^{\\circ}\\!-\\!(RT\/zF)\\mathop \\sum \\limits_i \\nu_i \\ln(a_i)\\] where \\(E_{\\rm{eq}}\\) is the equilibrium electrode potential, \\(E^{\\circ}\\) the standard electrode potential of the reaction, \\(R\\) the gas constant, \\(T\\) the thermodynamic temperature, \\(F\\) the Faraday constant, \\(z\\) the electron number of an electrochemical reaction, and \\(\\nu_{\\rm{i}}\\) are the stoichiometric coefficients (numbers of species) in the equation of the electrode reaction, positive for products and negative for reactants, while \\(a_{\\rm{i}}\\) represents the activities of the species involved (most usually ions).","notes":{"1":"For a solution containing oxidized (ox) and reduced (red) forms of a redox couple at activities \\(a_{\\rm{ox}}\\) and \\(a_{\\rm{red}}\\), respectively, the equilibrium electrode potential is \\[E_{\\rm{eq}} = E^{\\circ}\\!-\\!(RT\/zF)\\ln(a_{\\rm{red}}\/a_{\\rm{ox}})\\] where \\(E^{\\circ}\\) is the standard electrode potential of the redox couple.","2":"In analytical chemistry, concentrations, rather than activities, are often considered (see Note to formal electrode potential) \\[E_{\\rm{eq}} = E^{\\circ\\prime}\\!-\\!(RT\/zF)\\ln(c_{\\rm{red}}\/c_{\\rm{ox}})\\] where \\(E^{\\circ\\prime}\\) is the formal potential which can differ from the standard electrode potential owing to the influence of real conditions (pH, ionic strength, concentration of complex forming substances, etc.), and \\(c_{\\rm{red}}\\) and \\(c_{\\rm{ox}}\\) are the amount concentrations of reduced and oxidized species, respectively. At \\(\\pu{25^{\\circ}C}\\), and for practical purposes, this equation is often written as \\[E_{\\rm{eq}} \\approx E^{\\circ\\prime}\\!-\\!(0.0592\/z)\\log_{10}(c_{\\rm{red}}\/c_{\\rm{ox}})\\] where the factor \\(0.0592 \\approx (RT\/F)\/{\\rm{log}}_{10}(\\rm{e})\\) at \\(\\pu{298.15 K}\\)."},"links":[{"term":"electron number of an electrochemical reaction","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/09063"},{"term":"equilibrium electrode potential","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/09064"},{"term":"formal electrode potential","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/09065"}],"sources":["PAC, 2020, 92, 641. 'Terminology of Electrochemical Methods of Analysis (IUPAC Recommendations 2019)' on page 649 (https:\/\/doi.org\/10.1515\/pac-2018-0109)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/09068\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/09068\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/09068\/plain"},"citation":"Citation: 'Nernst 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.09068","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":"2026-05-11T21:53:45+00:00"}}