HL Extension
Definition of the SHE Baseline
Standard electrode potentials (\(E^\circ\)) provide a thermodynamic scale for comparing oxidising and reducing strengths of half-cells relative to the Standard Hydrogen Electrode (\(E^\circ = 0.00\text{ V}\)).
Standard Conditions
HL Extension
Standard Conditions for Potentials
- Temperature: 298 K (25 °C)
- Pressure of gases: 100 kPa (1 bar)
- Concentration of aqueous ions: 1.00 mol dm⁻³
- Platinum electrode (inert catalyst) for gas/ion half-cells
The Standard Hydrogen Electrode (SHE)
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 |
Examiner Trap
E° is an Intensive Property
\(E^\circ\) values are intensive properties (measured in volts = Joules per Coulomb). When multiplying half-equations by integers to balance electrons, never multiply \(E^\circ\)!
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