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

https://doi.org/10.1351/goldbook.D01860
The decrease in Gibbs energy on going from the reactants to the products of a chemical reaction (-ΔG).
Source:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1107 (https://doi.org/10.1351/pac199466051077)