Suraj Sir Chemistry

Electrochemical Cells

Galvanic cells turn a spontaneous redox reaction into electricity. The Daniell cell, the salt bridge, the batteries in your pocket, and the hydrogen fuel cell — with the electrode reactions for each.

The Daniell cell & salt bridge

Fig · Zn (anode, −) is oxidised and dissolves; Cu²⁺ is reduced onto the Cu cathode (+). Electrons flow Zn → Cu through the wire; the salt bridge carries ions to keep both solutions neutral.

The salt bridge — why it's essential

▪ Completes the circuit by letting ions flow between the half-cells (cations → cathode, anions → anode).

▪ Maintains electrical neutrality — the anode solution gains Zn²⁺, the cathode loses Cu²⁺; the bridge balances the charge.

▪ Prevents the liquid-junction potential and stops the two solutions mixing. Made of KCl / KNO₃ in agar-agar (ions of nearly equal mobility).

▪ Cell notation: Zn | Zn²⁺ (1 M) ‖ Cu²⁺ (1 M) | Cu. E°cell = E°(cathode) − E°(anode) = 0.34 − (−0.76) = 1.10 V.

Primary cells — used once, not rechargeable

Secondary cells — rechargeable

Fuel cell

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