The role of redox reactions in electrochemical cells is central, because they are the driving force that allows the cells to either generate electricity (in galvanic cells) or use electricity to drive reactions (in electrolytic cells).
In Galvanic (Voltaic) Cells
- The cell converts chemical energy → electrical energy.
- Oxidation happens at the anode → electrons are released.
- Reduction happens at the cathode → electrons are consumed.
- The movement of electrons through the external circuit produces electric current.
✔ Example: In a Daniell cell, zinc is oxidized (Zn → Zn²⁺ + 2e⁻) and copper ions are reduced (Cu²⁺ + 2e⁻ → Cu).
In Electrolytic Cells
- The cell converts electrical energy → chemical energy.
- The external power source forces non-spontaneous redox reactions to occur.
- Reduction takes place at the cathode, while oxidation occurs at the anode.
✔ Example: In the electrolysis of water, H⁺ ions are reduced to H₂ gas at the cathode, and OH⁻ ions are oxidized to O₂ gas at the anode.
Simple Summary
- Oxidation (loss of electrons) + Reduction (gain of electrons) = Redox reaction.
- Redox reactions are what allow electrochemical cells to either generate or use electricity.
Without redox reactions, electrochemical cells could not function at all.