Which of the following is not correct?

Options

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

Explanation

To determine which of the statements regarding Gibbs free energy (ΔG) is not correct, we need to analyze the properties of ΔG in relation to spontaneous and non-spontaneous reactions, as well as reversible reactions.

### Step-by-Step Solution:

1. **Understanding ΔG**:
- ΔG, or Gibbs free energy, is a thermodynamic potential that helps predict the spontaneity of a reaction.
- A negative ΔG indicates that a reaction is spontaneous, while a positive ΔG indicates that a reaction is non-spontaneous.

2. **Analyzing the Statements**:
- **Statement 1**: ΔG is zero for a reversible reaction.
- This statement is correct. For a reversible reaction at equilibrium, ΔG = 0.
- **Statement 2**: ΔG is negative for a spontaneous reaction.
- This statement is also correct. A spontaneous reaction is characterized by a negative ΔG.
- **Statement 3**: ΔG is positive for a spontaneous reaction.
- This statement is incorrect. A spontaneous reaction cannot have a positive ΔG; it must be negative.
- **Statement 4**: ΔG is positive for a non-spontaneous reaction.
- This statement is correct. Non-spontaneous reactions have a positive ΔG.

3. **Identifying the Incorrect Statement**:
- From our analysis, Statement 3 is not correct. It contradicts the fundamental principle that spontaneous reactions have a negative ΔG.

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

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