I. General Thermodynamic Treatment of Chemical Equilibrium

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 ln aj (1) where ∆Ḡ◦ is the molar Gibbs free energy at a reference state, taken to be the standard state. Now the change in the Gibbs free energy of the reaction is ∆rG = c∆ḠC + d∆ḠD − a∆ḠA − b∆ḠB