Galvanic and electrolytic cells are two major types of electrochemical cells that connect chemical reactions with electrical energy. A galvanic cell uses a spontaneous redox reaction to produce an electric current, like a battery. An electrolytic cell uses an external power source to force a nonspontaneous redox reaction, such as plating a metal or splitting molten salt.
Comparing them helps students keep track of electron flow, electrode signs, and energy changes.
Key Facts
- Oxidation occurs at the anode in both galvanic and electrolytic cells.
- Reduction occurs at the cathode in both galvanic and electrolytic cells.
- Galvanic cell: spontaneous reaction, chemical energy becomes electrical energy, Ecell > 0.
- Electrolytic cell: nonspontaneous reaction, electrical energy becomes chemical energy, Ecell < 0 without the power source.
- Standard cell potential: E°cell = E°cathode - E°anode.
- Gibbs free energy and cell voltage are related by ΔG = -nFEcell.
Vocabulary
- Galvanic cell
- A cell that converts energy from a spontaneous redox reaction into electrical energy.
- Electrolytic cell
- A cell that uses electrical energy from an external source to drive a nonspontaneous redox reaction.
- Anode
- The electrode where oxidation occurs and electrons are produced or removed from a substance.
- Cathode
- The electrode where reduction occurs and electrons are gained by a substance.
- Salt bridge
- A pathway containing ions that completes the circuit and keeps charge balanced between half-cells.
Common Mistakes to Avoid
- Calling the anode always negative is wrong because the anode is negative in a galvanic cell but positive in an electrolytic cell.
- Calling the cathode always positive is wrong because the cathode is positive in a galvanic cell but negative in an electrolytic cell.
- Reversing oxidation and reduction is wrong because oxidation always occurs at the anode and reduction always occurs at the cathode, no matter which type of cell is used.
- Forgetting charge balance in the solutions is wrong because ion movement through a salt bridge or electrolyte is needed to prevent charge buildup and keep current flowing.
Practice Questions
- 1 A galvanic cell uses Zn(s) | Zn2+(aq) and Cu2+(aq) | Cu(s). If E°red for Cu2+/Cu is +0.34 V and E°red for Zn2+/Zn is -0.76 V, calculate E°cell.
- 2 For the cell reaction involving 2 moles of electrons and Ecell = 1.10 V, calculate ΔG using ΔG = -nFEcell and F = 96485 C/mol e-.
- 3 A student sees bubbles forming at one electrode in a cell connected to a battery. Explain how to decide whether the cell is galvanic or electrolytic and identify which electrode is the anode.