Title: Raoult’s law
Long Title: IUPAC Gold Book - Raoult’s law
DOI: 10.1351/goldbook.15349
Status: current

Definition
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 \(\ce{B}\).

Note
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.

Related Term
- mixture: https://goldbook.iupac.org//terms/view/16270

Source
- PAC, 2008, 80, 233. 'Glossary of terms related to solubility (IUPAC Recommendations 2008)' on page 260 (https://doi.org/10.1351/pac200880020233)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/15349/html
- json: https://goldbook.iupac.org/terms/view/15349/json
- xml: https://goldbook.iupac.org/terms/view/15349/xml

Citation: 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
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Accessed: 2026-06-04T22:46:54+00:00