Question
What is the difference between a galvanic cell and an electrolytic cell? Explain with examples.
Solution — Step by Step
The fundamental question is: does the reaction happen on its own, or do we force it?
A galvanic cell runs on a spontaneous redox reaction — the chemicals want to react, and we harvest the electrical energy they release. A electrolytic cell does the opposite — we pump electrical energy in to force a non-spontaneous reaction to occur.
EMF (electromotive force) tells us the direction of energy flow.
In a galvanic cell, and EMF is positive — the cell produces voltage naturally. In an electrolytic cell, and we must apply external voltage greater than the cell’s back-EMF to drive the reaction forward.
Here’s the trick: the labels “anode” and “cathode” stay consistent (anode = oxidation, cathode = reduction), but the polarity flips between the two cells.
| Property | Galvanic Cell | Electrolytic Cell |
|---|---|---|
| Energy | Produces electrical energy | Consumes electrical energy |
| Reaction | Spontaneous | Non-spontaneous |
| EMF | Positive (+ve) | Applied externally |
| Anode charge | Negative (−) | Positive (+) |
| Cathode charge | Positive (+) | Negative (−) |
| Example | Daniel cell (Zn-Cu) | Electrolysis of water |
Galvanic cell example: The Daniel cell. Zinc dissolves at the anode (oxidation), copper deposits at the cathode (reduction). The cell produces ~1.1 V spontaneously. This is the same chemistry that powers batteries.
Electrolytic cell example: Electrolysis of acidified water. We apply ~2V externally — water does not break down on its own. Oxygen forms at the anode, hydrogen at the cathode.
Galvanic cell: Converts chemical energy → electrical energy (spontaneous).
Electrolytic cell: Converts electrical energy → chemical energy (non-spontaneous).
Why This Works
The underlying physics here is Gibbs free energy. When is negative, the reaction releases energy — and we can channel that energy as electrical work. That’s the galvanic cell.
When is positive, the system won’t react unless we supply energy from outside. We use an external battery or power source to push electrons in the “wrong” direction, forcing the non-spontaneous reaction to proceed. That’s electrolysis.
The anode polarity flip is the most conceptually interesting part. In a galvanic cell, the anode is the negative terminal because electrons are being pushed out of it (oxidation releases electrons into the wire). In an electrolytic cell, the anode is connected to the positive terminal of the external source — that positive charge pulls electrons away from the electrode, causing oxidation at the anode. Same chemistry, opposite wiring.
Alternative Method
For MCQs, use this elimination trick instead of recalling definitions:
If the question mentions “external EMF applied” or “current passed through” — it’s an electrolytic cell. If it mentions “EMF generated” or “cell potential” — it’s a galvanic cell. This catches ~90% of NCERT-pattern MCQs instantly.
Another angle: look at the anode polarity. If anode is negative → galvanic. If anode is positive → electrolytic. This is the single most-tested MCQ fact from this chapter in CBSE and JEE Main.
Common Mistake
Students flip the anode polarity in one of the two cells — usually writing “anode is positive in galvanic cell.” The memory trick: in a galvanic cell, the anode is negative — remember GN (galvanic = negative anode). Everything else follows from this.
Also, don’t write “electrolytic cells have negative EMF.” The EMF of the cell being driven is still calculated as positive — what’s negative is of the applied reaction if you reverse it. The NCERT phrasing is simply “external source of EMF is required.”