Electrochemistry is worth 5–7 marks and almost always includes a Nernst or Faraday numerical. Learn these formulas and the sign conventions.
Galvanic cell basics
- Anode: oxidation (−), Cathode: reduction (+). Cell notation: anode ‖ cathode.
- E°cell = E°cathode − E°anode
- ΔG° = −nFE°cell; ΔG° = −2.303RT log K
Nernst equation (298 K)
Ecell = E°cell − (0.059/n) log Q, Q = [products]/[reactants] (ions only).
Example: Zn | Zn²⁺(0.1 M) ‖ Cu²⁺(1 M) | Cu, E° = 1.10 V. E = 1.10 − (0.059/2) log(0.1/1) = 1.10 + 0.0295 = 1.13 V.
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Conductance
- Conductance G = 1/R; conductivity κ = G × (l/A)
- Molar conductivity Λm = κ × 1000/M (S cm² mol⁻¹)
- Kohlrausch: Λ°m = ν₊λ°₊ + ν₋λ°₋; degree of dissociation α = Λm/Λ°m
Faraday’s laws
- m = ZIt; Z = M/nF; F = 96500 C/mol
- Example: charge to deposit 1 mol Al from Al³⁺ = 3 F = 289500 C
- Example: 0.5 A for 1 h through Cu²⁺: m = (63.5/2 × 96500) × 0.5 × 3600 = 0.59 g
Common mistakes
- Adding electrode potentials instead of subtracting
- Using n wrong in the Nernst equation
- Forgetting units of molar conductivity
Related: Chemical Kinetics formulas.
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Frequently asked questions
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