Term: kinetic activity factor
https://doi.org/10.1351/goldbook.K03396

Definition:
A factor involving activity coefficients that appears as a multiplier in the rate equation. For a bimolecular reaction the factor is \[\frac{y_{\text{A}}\ y_{\text{B}}}{y_{\ddagger}}\] where y A, y B and y ‡ are the activity coefficients for the reactants A and B and the activated complex, respectively. For a unimolecular reaction the factor is \[\frac{y_{\text{A}}}{y_{\ddagger}}\] and for a trimolecular reaction it is \[\frac{y_{\text{A}}\ y_{\text{B}}\ y_{\text{C}}}{y_{\ddagger}}\]

Related Terms:
1) bimolecular (http://doi.org/10.1351/goldbook.M03989-1).
2) activated complex (http://doi.org/10.1351/goldbook.A00092).
3) unimolecular (http://doi.org/10.1351/goldbook.M03989-2).

Source: PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 171 (https://doi.org/10.1351/pac199668010149)

Citation: 'kinetic activity factor' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.K03396

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