15349 IUPAC Gold Book - Raoult’s law 10.1351/goldbook.15349 15349 current 1 Fugacity (\(\tilde{p}_{\ce{B}}\)) of a gaseous component (\(\ce{B}\)) in equilibrium with a liquid or solid mixture containing \(\ce{B}\) is directly proportional to the activity (\(a_{\ce{B}}\)) of the component in the mixture \[\tilde{p}_{\ce{B}} = \tilde{p}_{\ce{B}}^{\ast} f_{\ce{B}} x_{\ce{B}}\] where \(f_{\ce{B}}\) is the activity coefficient of \(\ce{B}\) referenced to Raoult’s law at mole fraction \(x_{\ce{B}}\) and \(\tilde{p}_{\ce{B}}\) is the fugacity of pure \(\ce{B}\). An ideal mixture is defined by replacing fugacities with partial pressures and setting the activity coefficient equal to unity \[p_{\ce{B}} = p_{\ce{B}}^{\ast} x_{\ce{B}} = y_{\ce{B}}p\] The total pressure, \(p\), is then simply the sum of the partial pressures of all components. mixture https://goldbook.iupac.org//terms/view/16270 PAC, 2008, 80, 233. 'Glossary of terms related to solubility (IUPAC Recommendations 2008)' on page 260 (https://doi.org/10.1351/pac200880020233) https://goldbook.iupac.org/terms/view/15349/html https://goldbook.iupac.org/terms/view/15349/json https://goldbook.iupac.org/terms/view/15349/plain Citation: 'Raoult’s law' 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.15349 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. 2026-06-28T13:10:28+00:00