Which of the following is not correct

Options

A. `Delta G` is zero for a reversible reaction
B. `Delta G` is positive for a spontaneous reaction
C. `Delta G` is negative for a spontaneous reaction
D. `Delta G` is positive for a non-spontaneous reaction

Explanation

To determine which statement is not correct, we will analyze each statement regarding Gibbs free energy (ΔG) and its relation to spontaneous and non-spontaneous reactions.

1. **Statement 1: ΔG is zero for a reversible reaction.**
- A reversible reaction is at equilibrium. At equilibrium, the Gibbs free energy change (ΔG) is indeed zero. Therefore, this statement is **correct**.

2. **Statement 2: ΔG is positive for a spontaneous reaction.**
- For a reaction to be spontaneous, it must occur without the need for external energy. This is characterized by a negative ΔG. Therefore, this statement is **not correct**.

3. **Statement 3: ΔG is negative for a spontaneous reaction.**
- As mentioned, spontaneous reactions have a negative ΔG. Thus, this statement is **correct**.

4. **Statement 4: ΔG is positive for a non-spontaneous reaction.**
- Non-spontaneous reactions require external energy to proceed, which corresponds to a positive ΔG. Hence, this statement is **correct**.

**Conclusion:**
The statement that is not correct is **Statement 2: ΔG is positive for a spontaneous reaction.**