Question

A galvanic cell functions like an electrolytic cell when :

• A. \( E_{cell} = E_{ext} \)
• B. \( E_{cell} > E_{ext} \)
• C. \( E_{ext} > E_{cell} \)
• D. \( E_{cell} = 0 \)

Hint:

When the opposing external voltage exceeds the emf of the cell, the cell reaction reverses and the cell works as an electrolytic cell.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
A galvanic cell turns chemical energy into electrical energy. Its own emf drives the electrons.
An electrolytic cell does the opposite. An outside source forces a reaction that would not occur by itself.

Step 2: Key Formula or Approach:
Compare the cell emf \( E_{cell} \) with the opposing external voltage \( E_{ext} \) applied across the electrodes.
The larger of the two decides the direction of the cell reaction.

Step 3: Detailed Explanation:
For a Daniell cell, \( E_{cell} = 1.1 \text{ V} \).
If \( E_{ext} \) is below 1.1 V, the cell still works as a galvanic cell and the current flows from its own emf.
If \( E_{ext} \) equals 1.1 V, there is no net change and no current flows.
If \( E_{ext} \) rises above 1.1 V, the external source wins. The reactions at the electrodes reverse, and the cell acts as an electrolytic cell.

Step 4: Why the other options are wrong.
(A) \( E_{cell} = E_{ext} \): the two balance, so the cell is at equilibrium.
(B) \( E_{cell} > E_{ext} \): the cell is still the stronger one, so it stays galvanic.
(D) \( E_{cell} = 0 \): this means a dead cell at equilibrium and does not give a reversed reaction.

Final Answer:
The galvanic cell acts as an electrolytic cell when the external voltage is greater than the cell emf. \[ \boxed{E_{ext} > E_{cell}} \]