kinetic activity factor

A factor involving activity coefficients that appears as a multiplier in the rate equation. For a bimolecular reaction the factor is
y A y B y ‡,
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
y A y ‡,
and for a trimolecular reaction it is
y A y B y C y ‡.
PAC, 1996, 68, 149 (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 171