Question

The standard electrode potential for Daniell cell is 1.1 V. Calculate the standard Gibbs energy change for the reaction:

Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

Hint:

Always check the sign. A spontaneous redox reaction (like in a galvanic cell) must have a positive E°cell and a negative ΔG°. Ensure the units are consistent. Usually, the formula gives the value in joules, so divide by 1000 to convert it into kilojoules.

Answer 1

Concept:
The relationship between the standard Gibbs free energy change (ΔG°) and the standard electromotive force (E°cell) of a cell is given by:

ΔG° = −nFE°cell

Where:
n = number of moles of electrons transferred
F = Faraday constant ≈ 96487 C/mol
E°cell = standard electrode potential of the cell

Step 1: Determine the number of electrons transferred (n).
Cell reaction:
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

Oxidation: Zn(s) → Zn2+(aq) + 2e−
Reduction: Cu2+(aq) + 2e− → Cu(s)

Thus, n = 2.

Step 2: Calculate ΔG°.
ΔG° = −nFE°cell

ΔG° = −2 × 96487 × 1.1

ΔG° = −212271.4 J/mol

ΔG° ≈ −212.27 kJ/mol