Galvanic cell vs electrolytic cell — complete comparison with cell diagrams

Question

Compare galvanic cells and electrolytic cells. What are the differences in energy conversion, electrode polarity, and spontaneity?

Solution — Step by Step

A galvanic cell (voltaic cell) converts chemical energy to electrical energy. The reaction is spontaneous ( $\Delta G < 0$ ) — it generates electricity on its own.

An electrolytic cell converts electrical energy to chemical energy. The reaction is non-spontaneous ( $\Delta G > 0$ ) — we force it to happen using an external power source.

Think of it this way: a galvanic cell is like a battery powering a torch. An electrolytic cell is like charging that battery.

In a galvanic cell:

Anode = negative terminal (oxidation occurs, electrons leave from here)
Cathode = positive terminal (reduction occurs, electrons arrive here)

In an electrolytic cell:

Anode = positive terminal (connected to + of battery)
Cathode = negative terminal (connected to - of battery)

The chemistry is the same (oxidation at anode, reduction at cathode) — but the polarity reverses.

A galvanic cell uses a salt bridge (KCl or KNO3 in agar) to maintain electrical neutrality and complete the circuit.

Daniel cell notation: $\text{Zn}(s) | \text{Zn}^{2+}(aq) || \text{Cu}^{2+}(aq) | \text{Cu}(s)$

An electrolytic cell has no salt bridge — both electrodes dip into the same electrolyte solution, and an external battery drives the current.

graph LR
    subgraph Galvanic Cell
        A1["Anode (-): Zn oxidised"] -->|electrons| B1["Cathode (+): Cu2+ reduced"]
        A1 -.->|salt bridge| B1
    end
    subgraph Electrolytic Cell
        C1["Battery +"] --> D1["Anode (+): oxidation"]
        C1 --> E1["Cathode (-): reduction"]
        D1 -.->|same solution| E1
    end

Why This Works

Feature	Galvanic Cell	Electrolytic Cell
Energy conversion	Chemical $\to$ Electrical	Electrical $\to$ Chemical
Spontaneity	Spontaneous ( $\Delta G < 0$ )	Non-spontaneous ( $\Delta G > 0$ )
$E°_{cell}$	Positive	Negative (forced by external EMF)
Anode polarity	Negative	Positive
Cathode polarity	Positive	Negative
Salt bridge	Present	Absent
Solutions	Two separate half-cells	Usually one electrolyte
Example	Daniel cell, dry cell	Electroplating, electrolysis of water

The reason the polarity flips is intuitive: in a galvanic cell, electrons naturally leave the anode (making it negative). In an electrolytic cell, the battery pushes electrons toward the cathode (making it negative) and pulls electrons from the anode (making it positive).

In both cells, oxidation always happens at the anode and reduction always happens at the cathode. This is a universal truth — OILRIG (Oxidation Is Loss, Reduction Is Gain) applies everywhere.

Alternative Method

A memory trick for polarity:

Galvanic: “AN OX” — Anode Negative, OXidation. The anode is where electrons are produced, so it is the negative terminal.

Electrolytic: The battery’s positive terminal attracts electrons away from the anode, making the anode positive. The battery’s negative terminal pushes electrons to the cathode, making it negative.

Common Mistake

The most tested confusion: students assume “anode is always positive.” This is only true in electrolytic cells. In galvanic cells, the anode is the negative terminal. NEET and JEE both test this — a question might give a cell setup and ask “which electrode is positive?” Always check whether the cell is galvanic or electrolytic before answering.

Question

Solution — Step by Step

Why This Works

Alternative Method

Common Mistake

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