If the ΔG value of a reaction is negative, what is true of the ΔG value of the reverse reaction?

A. ΔG > 0

B. ΔG < 0

C. ΔG = 0

D. ΔG fluctuates

In physical chemistry and thermodynamics, the Gibbs free energy or ΔG is very important because it is the criterion for spontaneity. When the magnitude of ΔG is negative, the reaction is spontaneous. This means that the reaction readily occurs. When the magnitude is positive, the reaction is non-spontaneous. This means that in order for the reaction to proceed, you must apply external force like electricity.

For equilibrium reactions, there is a forward and reverse reaction written as: A + B ⇆ C. Only one of those reactions is spontaneous. So, if the forward reaction is - ΔG, then the reverse reaction is the opposite which is + ΔG. The answer is letter A.