9.7 Galvanic (Voltaic) and Electrolytic Cells

Galvanic (Voltaic) Cells

A galvanic cell uses a spontaneous redox reaction (ΔG < 0, E°cell > 0) to generate electrical energy. Oxidation occurs at the anode, reduction occurs at the cathode — remember "red cat, an ox." Electrons flow through the external wire from anode to cathode, while a salt bridge allows ion flow to maintain electrical neutrality in each half-cell.

Electrolytic Cells

An electrolytic cell uses an external power source to force a nonspontaneous redox reaction (ΔG > 0, E°cell < 0). Electrolysis can decompose compounds or electroplate metals. The anode and cathode designations stay the same (oxidation at anode, reduction at cathode), but the power source pushes electrons in the reverse direction compared to a galvanic cell.

Cell Diagrams and Electron Flow

In both cell types, electrons flow through the external circuit, never through the solution. In a galvanic cell, the anode is negative and cathode is positive; in an electrolytic cell, this polarity is reversed because the battery forces current in the opposite direction. Mass of the anode decreases (metal oxidizes/dissolves) while mass of the cathode increases (ions reduce and deposit) in many metal-based cells.

Key terms

Galvanic (Voltaic) Cell

Uses a spontaneous redox reaction (E°cell > 0, ΔG < 0) to produce electrical energy.

Electrolytic Cell

Uses an external power source to drive a nonspontaneous redox reaction (E°cell < 0, ΔG > 0).

"Red Cat, An Ox"

Mnemonic: REDuction occurs at the CAThode; OXidation occurs at the ANode.

Electrode Polarity in Galvanic Cells

Anode is negative; cathode is positive — electrons flow from anode to cathode through the wire.

Electrode Polarity in Electrolytic Cells

Anode is positive; cathode is negative — reversed from galvanic cells due to the external power source.

Try an AP-style question

In a galvanic cell, where does oxidation occur?

1. In the salt bridge
2. At the cathode
3. At the anode
4. In the external wire