The free energy change due to a reaction is zero when

Options

A. The reactants are initially mixed
B. A catalyst is added
C. The system is at equilibrium
D. The reactants are completely consumed

Answer

To solve the question regarding when the free energy change (ΔG) due to a reaction is zero, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Free Energy (ΔG)**:
- Free energy change (ΔG) is a thermodynamic quantity that helps predict the spontaneity of a reaction.

2. **Identify the Conditions for ΔG**:
- ΔG < 0: The reaction is spontaneous.
- ΔG > 0: The reaction is non-spontaneous.
- ΔG = 0: The system is at equilibrium.

3. **Analyze the Given Statement**:
- The question states that the free energy change due to a reaction is zero (ΔG = 0). This indicates that the reaction is at equilibrium.

4. **Evaluate the Options**:
- **Option A**: The reactants are initially mixed.
- This does not imply anything about the free energy change; it is incorrect.
- **Option B**: A catalyst is used.
- A catalyst speeds up the reaction but does not affect the free energy change; it is incorrect.
- **Option C**: The system is at equilibrium.
- This is correct because ΔG = 0 indicates that the reaction is at equilibrium.
- **Option D**: The reactants are completely consumed.
- This does not necessarily mean that ΔG is zero; it is incorrect.

5. **Conclusion**:
- The correct answer is **Option C: The system is at equilibrium**.