Consider an equilibrium reaction aA+ bB ⇀↽ cC+ dD We do not specify any phases, as we will treat the reaction generally using activities. An equilibrium reaction is one that can proceed in both directions, as indicated by the ⇀↽ symbol replacing the usual −→ in the chemical equation. Recall that the molar free energy ∆Ḡj for compound j in the reaction in terms of its activity aj as ∆Ḡ = ∆Ḡ◦ +RT...