At 298 K, a chemist records the standard free-energy changes for four gas-phase reactions that all involve 1 mol of reactant converting to products in the stoichiometric amounts shown.
Table 1 – Standard free-energy changes at 298 K
Reaction I ΔG° = −25.0 kJ·mol⁻¹
Reaction II ΔG° = +12.0 kJ·mol⁻¹
Reaction III ΔG° = −1.5 kJ·mol⁻¹
Reaction IV ΔG° = 0.0 kJ·mol⁻¹
(a) Rank the four reactions from the one with the largest equilibrium constant to the one with the smallest equilibrium constant. If any reactions are expected to have essentially the same equilibrium constant, indicate that clearly in your ranking.
(b) Provide a clear chemical justification for the order you listed in part (a), making explicit reference to the relationship between the sign and magnitude of ΔG° and the extent to which products or reactants are favored at equilibrium.