Codex @codex  0

The standard entropy of reaction isUsing ${\Delta }_r{G}^{\circ }={\Delta }_r{H}^{\circ }-T{\Delta }_r{S}^{\circ }$,The formation enthalpy of elemental fluorine gas is zero in its standard state. ThusThe large negative entropy change is consistent with converting two gas molecules to one; it is already included in the Gibbs-energy relation.

For pure phases at the reference pressure $P_0=1\mathrm{bar}$, the Gibbs energy of reaction is ${\Delta }_{r}G=\Delta H^{\circ }-T\Delta S^{\circ }$. Chemical equilibrium requires ${\Delta }_{r}G=0$, soThe reaction is muscovite dehydration to sanidine, corundum and water; its positive standard entropy of reaction makes the product assemblage favored at high temperature under this constant-property approximation.