The cell reaction as written is spontaneous if the cell potential is:

Options

A. Positive
B. Negative
C. Zero
D. Infinite

Explanation

To determine when a cell reaction is spontaneous, we need to analyze the relationship between the cell potential (E_cell) and Gibbs free energy (G). The spontaneity of a reaction can be assessed using the following steps:

### Step-by-Step Solution:

1. **Understanding Gibbs Free Energy (G)**:
- The Gibbs free energy change (ΔG) is a thermodynamic potential that can predict the spontaneity of a reaction. A reaction is spontaneous if ΔG is negative.

2. **Relation between Gibbs Free Energy and Cell Potential**:
- The relationship between Gibbs free energy and cell potential is given by the equation:
\[ \Delta G = -nFE_{cell} \]
where:
- \( \Delta G \) = change in Gibbs free energy
- \( n \) = number of moles of electrons transferred
- \( F \) = Faraday's constant (approximately 96485 C/mol)
- \( E_{cell} \) = cell potential

3. **Analyzing the Equation**:
- From the equation, we can see that:
- If \( E_{cell} \) is positive, then \( \Delta G \) will be negative (since -nF is always negative), indicating a spontaneous reaction.
- If \( E_{cell} \) is zero, then \( \Delta G \) will also be zero, indicating that the system is at equilibrium.
- If \( E_{cell} \) is negative, then \( \Delta G \) will be positive, indicating a non-spontaneous reaction.

4. **Conclusion**:
- Therefore, for the cell reaction to be spontaneous, the cell potential \( E_{cell} \) must be positive.

### Final Answer:
The cell reaction is spontaneous if the cell potential is **positive**.