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Redox Chemistry

Topic 6 of 6

Use a reaction to generate electricity

A simple cell converts chemical energy into electrical energy.

O-Level 6092 (2026) / SEC G3 K324 (2027)

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Pure only

Use a reaction to generate electricity

A simple cell converts chemical energy into electrical energy.

A simple cell contains two different electrodes in an electrolyte connected through an external circuit. A more reactive metal tends to lose electrons more readily. In a zinc/copper cell using dilute acid, zinc is oxidised: Zn(s) -> Zn2+(aq) + 2e-. Electrons travel through the wire towards copper, where hydrogen ions can gain them: 2H+(aq) + 2e- -> H2(g). The electrolyte carries ionic current and completes the circuit.

Electron flow in a simple cell

Zinc loses electrons that flow through the external wire to copper; hydrogen ions accept electrons at the copper surface.

Schematic simple cell; electron flow is in the external conductor, not through the solution.

Hydrogen can be obtained from water by electrolysis or from hydrocarbons. In a hydrogen fuel cell it reacts with oxygen to produce water and electricity directly: 2H2(g) + O2(g) -> 2H2O(l). Water is the point-of-use product, but overall environmental impact depends on how the hydrogen and electricity were produced. Detailed fuel-cell construction is not required.

Check your understandingHow does a simple cell differ from electrolysis in energy direction?Think it through, then reveal the answer
A cell uses a spontaneous chemical reaction to supply electrical energy. Electrolysis uses an external electrical supply to drive chemical change. In both, oxidation is electron loss and reduction is electron gain.