affinity of reaction, \(A\)

https://doi.org/10.1351/goldbook.A00178
Negative partial derivative of Gibbs energy with respect to extent of reaction at constant pressure and temperature. It is positive for spontaneous reactions.
See also: driving force
Source:
Green Book, 2nd ed., p. 49 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)