Title: absolute activity
Long Title: IUPAC Gold Book - absolute activity
DOI: 10.1351/goldbook.A00019
Status: current
Index: quantity

Definition
The exponential of the ratio of the chemical potential, \(\mu\), to \(R\,T\) where \(R\) is the gas constant and \(T\) the thermodynamic temperature, \(\lambda=\rm{e}^{\,\mu/RT}\).

Related Terms
- chemical potential: https://goldbook.iupac.org//terms/view/C01032
- gas constant: https://goldbook.iupac.org//terms/view/G02579
- thermodynamic temperature: https://goldbook.iupac.org//terms/view/T06321

Source
- Green Book, 2nd ed., p. 40 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)

Related References
- PAC, 1984, 56, 567. 'Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Recommendations 1983)' on page 569 (https://doi.org/10.1351/pac198456050567)
- PAC, 1996, 68, 957. 'Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)' on page 959 (https://doi.org/10.1351/pac199668040957)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/A00019/html
- json: https://goldbook.iupac.org/terms/view/A00019/json
- xml: https://goldbook.iupac.org/terms/view/A00019/xml

Citation: Citation: 'absolute activity' 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.A00019
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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: 2026-04-27T16:01:13+00:00