Title: activity coefficient at infinite dilution
Long Title: IUPAC Gold Book - activity coefficient at infinite dilution
DOI: 10.1351/goldbook.15312
Status: current

Definition
For a substance \(\ce{B}\), activity coefficient \(f_{\ce{B}}\) extrapolated to infinite dilution: \[\ln (f_{\ce{B}}^{\infty}) = \lim \limits_{x_{\ce{B}} \to 0} (\frac{\mu_{\ce{B}} - \mu_{\ce{B}}^{\ast}}{RT} - \ln x_{\ce{B}})\]

Notes
1) Useful for dilute mixtures as an alternative to the standard chemical potential on a molality basis.
2) The relation between the activity coefficient at infinite dilution and the standard chemical potentials is, for a solute \(\ce{B}\) in a solvent \(\ce{A}\), \[\ln f_{\ce{B}}^{\infty} = \frac{\mu_{m,\ce{B}}^{_{^⦵\!}} - \mu_{\ce{B}}^{\ast}}{RT} - \ln (M_{\ce{A}}m_{\ce{B}}^{_{^⦵\!}})\] where \(M_{\ce{A}}\) is the molar mass of the solvent.

Related Terms
- infinite dilution: https://goldbook.iupac.org//terms/view/15333
- mixtures: https://goldbook.iupac.org//terms/view/16270

Source
- PAC, 2008, 80, 233. 'Glossary of terms related to solubility (IUPAC Recommendations 2008)' on page 237 (https://doi.org/10.1351/pac200880020233)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/15312/html
- json: https://goldbook.iupac.org/terms/view/15312/json
- xml: https://goldbook.iupac.org/terms/view/15312/xml

Citation: Citation: 'activity coefficient at infinite dilution' 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.15312
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Accessed: 2026-07-25T05:19:55+00:00