An electrochemical cell an behave like an electrolytic cell when

Options

A. `E_"cell" =0`
B. `E_"cell" gt E_"ext"`
C. `E_"ext" gt E_"cell"`
D. `E_"cell" = E_"ext"`

Answer

To determine when an electrochemical cell behaves like an electrolytic cell, we need to analyze the relationship between the cell potential (E_cell) and the external voltage (E_external). Here's a step-by-step solution:

### Step 1: Understand the Definitions
- **Electrochemical Cell**: A device that converts chemical energy into electrical energy (e.g., galvanic cell).
- **Electrolytic Cell**: A device that uses electrical energy to drive a non-spontaneous chemical reaction.

### Step 2: Analyze the Conditions
1. **When E_cell = 0**: This indicates that there is no net driving force for the reaction. The cell is at equilibrium.
2. **When E_cell < E_external**: The external voltage is greater than the cell potential, which means that the external energy can drive the reaction in the reverse direction, making the electrochemical cell behave like an electrolytic cell.
3. **When E_cell > E_external**: The cell can operate normally, generating electrical energy from a spontaneous reaction.
4. **When E_cell = E_external**: The reaction is at equilibrium, and no net current flows.

### Step 3: Identify the Key Condition
The key condition for an electrochemical cell to behave like an electrolytic cell is when the external voltage (E_external) exceeds the cell potential (E_cell). This allows the external energy to drive the reaction in the opposite direction.

### Conclusion
An electrochemical cell behaves like an electrolytic cell when:
- **E_external > E_cell**

Thus, the correct answer is that an electrochemical cell behaves like an electrolytic cell when the external voltage is greater than the cell potential.