Final answer:
Reversing a reaction changes the sign of the standard free energy change (ΔG°).
Step-by-step explanation:
When a reaction is reversed, the sign of the standard free energy change (ΔG°) is also reversed. If the original reaction has a positive ΔG°, meaning it is not spontaneous, reversing the reaction will make ΔG° negative, indicating that the reaction is now spontaneous. Conversely, if the original reaction has a negative ΔG°, meaning it is spontaneous, reversing the reaction will make ΔG° positive, indicating that the reverse reaction is not spontaneous.