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@.