At equilibrium, ∆G equals what?

At equilibrium, ∆G equals what?

• A. 0
• B. ∞
• C. ∆G°
• D. Negative value

Answer: (A)

At constant temperature and pressure, the driving force for a reaction is given by ΔG = ΔG° + RT ln Q. At equilibrium there is no net driving force, so ΔG = 0. This happens because Q equals the equilibrium constant K, and ΔG° is related to K by ΔG° = -RT ln K. Substituting Q = K into the equation gives ΔG = (-RT ln K) + RT ln K = 0. So the system’s free energy is minimized for the given conditions, and there’s no further tendency for the reaction to proceed in either direction. The other options imply a continuing drive or an undefined condition, which does not describe a system at equilibrium.

At constant temperature and pressure, the driving force for a reaction is given by ΔG = ΔG° + RT ln Q. At equilibrium there is no net driving force, so ΔG = 0. This happens because Q equals the equilibrium constant K, and ΔG° is related to K by ΔG° = -RT ln K. Substituting Q = K into the equation gives ΔG = (-RT ln K) + RT ln K = 0. So the system’s free energy is minimized for the given conditions, and there’s no further tendency for the reaction to proceed in either direction. The other options imply a continuing drive or an undefined condition, which does not describe a system at equilibrium.