📘 IB Understanding
Standard electrode potentials (E°) measure the tendency of a half-cell to undergo reduction, measured relative to the standard hydrogen electrode under standard conditions.
Standard Conditions
- Temperature: 298 K (25 °C)
- Concentration: 1.00 mol dm⁻³
- Pressure: 100 kPa (or 1 atm)
The Standard Hydrogen Electrode (SHE)
\(2\text{H}^+(\text{aq}) + 2\text{e}^- \rightleftharpoons \text{H}_2(\text{g})\)
\(E^\circ = 0.00 \text{ V (by definition)}\)
The SHE consists of a platinum electrode in 1.00 mol dm⁻³ H⁺(aq) with H₂ gas at 100 kPa bubbled over it. All other E° values are measured relative to this.
Key E° Values
| Half-Reaction (Reduction) | E° / V |
|---|---|
| Li⁺ + e⁻ ⇌ Li | -3.04 |
| Zn²⁺ + 2e⁻ ⇌ Zn | -0.76 |
| Fe²⁺ + 2e⁻ ⇌ Fe | -0.44 |
| 2H⁺ + 2e⁻ ⇌ H₂ | 0.00 |
| Cu²⁺ + 2e⁻ ⇌ Cu | +0.34 |
| Ag⁺ + e⁻ ⇌ Ag | +0.80 |
| F₂ + 2e⁻ ⇌ 2F⁻ | +2.87 |
📋 Exam Tip
E° values are intensive properties. They do not change when you multiply the half-equation by a coefficient. E° for Cu²⁺/Cu is always +0.34 V whether you write 1 or 2 moles.