## standard reaction quantities

https://doi.org/10.1351/goldbook.S05923
Infinitesimal changes in thermodynamic functions with @E02283@ divided by the infinitesimal increase in the extent when all the reactants and products are in their standard states. For the quantity $$X$$ they should be denoted by $$\Delta _{\text{r}}X^{\,\unicode{x26ac}}$$, but usually only $$\Delta X^{\,\unicode{x26ac}}$$ 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 @A00093@.
Source:
Green Book, 2nd ed., p. 52 [Terms] [Book]