driving force (affinity) of a reaction, \(A\)

The decrease in Gibbs energy on going from the reactants to the products of a chemical reaction (-ΔG).
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1107 (https://doi.org/10.1351/pac199466051077)
See also:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2237 (https://doi.org/10.1351/pac199668122223)