This Additional Higher Level mini-lesson covers Reactivity 3.2: standard electrode potentials, E°cell and feasibility, ΔG° = −nFE°, and quantitative electrolysis.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.
AHL — Reactivity 3.2
Standard electrode potentials
Each half-cell has a standard electrode (reduction) potential E°, measured against the standard hydrogen electrode (defined as 0.00 V) at 298 K, 100 kPa and 1 mol dm⁻³. A more positive E° means a stronger tendency to be reduced.
AHL — Reactivity 3.2
Cell potential and feasibility
Combine two half-cells:
E°cell = E°(cathode) − E°(anode)a reaction is feasible (spontaneous) when E°cell > 0
The half-cell with the more positive E° is reduced (cathode); the other is oxidised (anode).
AHL calculate
Cell potential
1Using E°(Cu²⁺/Cu) = +0.34 V and E°(Zn²⁺/Zn) = −0.76 V, calculate E°cell for the Zn–Cu cell.
V
Cu is the cathode: E°cell = 0.34 − (−0.76).
AHL — Reactivity 3.2
Linking E° to Gibbs energy
Cell potential connects directly to spontaneity:
ΔG° = −nFE°celln = moles of electrons, F = 96 500 C mol⁻¹
A positive E°cell gives a negative ΔG° — a feasible cell.
AHL calculate
Gibbs energy of the cell
2For the Zn–Cu cell (n = 2, E°cell = 1.10 V), calculate ΔG° in kJ (F = 96 500 C mol⁻¹).