Overview
This lecture explains how galvanic (voltaic) cells work by harnessing redox reactions to generate electrical energy, detailing cell setup, electron flow, and related terminology.
Redox Reactions and Electron Flow
- Redox involves paired reduction (gain of electrons) and oxidation (loss of electrons) reactions.
- The mnemonic "LEO the lion says GER" helps remember: Loss of Electrons is Oxidation, Gain of Electrons is Reduction.
- When reactants are separated and electrons move via a wire, electricity is produced.
Galvanic (Voltaic) Cell Structure
- A galvanic cell consists of two half-cells, each with a metal electrode in a solution of its ions.
- Common example: zinc electrode in zinc sulfate solution, copper electrode in copper sulfate solution.
- Electrodes are connected externally by a metal wire to allow electron flow.
Half-Reactions in the Galvanic Cell
- Anode (zinc): Zn(s) → Zn²⁺(aq) + 2e⁻ (oxidation).
- Cathode (copper): Cu²⁺(aq) + 2e⁻ → Cu(s) (reduction).
- Electrons flow from anode (zinc) to cathode (copper) through the wire.
Role of Salt Bridge
- A salt bridge or porous membrane maintains electrical neutrality by letting ions move between the half-cells.
- It prevents buildup of charge that would stop electron flow.
Electrode Naming and Charges
- The anode is where oxidation occurs and is negatively charged.
- The cathode is where reduction occurs and is positively charged.
- Electrons, being negative, are repelled by the anode and attracted to the cathode.
Cell Diagram Representation
- The cell diagram condenses the setup: Zn(s) | Zn²⁺ (aq) || Cu²⁺(aq) | Cu(s).
- Single lines indicate phase boundaries; double line indicates the salt bridge.
Key Terms & Definitions
- Redox Reaction — A chemical reaction involving transfer of electrons, with oxidation and reduction parts.
- Anode — The electrode where oxidation occurs (loses electrons), negative in a galvanic cell.
- Cathode — The electrode where reduction occurs (gains electrons), positive in a galvanic cell.
- Salt Bridge — A device allowing ion flow to preserve charge neutrality in the cell.
- Cell Diagram — Notation representing the composition and reactions of a galvanic cell.
Action Items / Next Steps
- Review the next lecture/video on electrolytic cells.
- Practice drawing cell diagrams and identifying anode/cathode in different setups.