https://doi.org/10.1351/goldbook.S05923
Infinitesimal changes in thermodynamic functions with they should be denoted by , but usually only is used. For specific types of reactions the subscript r is replaced by: f for formation, c for combustion, a for atomization and superscript ‡ for
extent of reaction
divided by the infinitesimal increase in the extent when all the reactants and products are in their standard states. For the quantity activation
.