Question

How do you calculate galvanic cell potential?

Answer 1

You calculate a galvanic cell potential from the potentials of the half-reactions.

E°cell = E°red + E°ox

1. Write the reduction and oxidation half-reactions for the celll.

2. Look up the reduction potential, E°red, for the reduction half-reaction.

3. Look up the reduction potential for the reverse of the oxidation half-reaction. Reverse the sign (E°ox = - E°red).

4. Add the two half-cell potentials to get the cell potential.

E°cell = E°red + E°ox

EXAMPLE:

Find the standard cell potential for the following galvanic cell.

Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

a. Write the half-reactions for each process.

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

b. Look up the standard potential for the reduction half-reaction.

Cu²⁺(aq) + 2e⁻ → Cu(s) E°red = +0.339 V

c. Look up the standard reduction potential for the reverse of the oxidation reaction. Change the sign.

Zn(s) → Zn²⁺(aq) + 2e⁻ E°ox = +0.762 V

d. Add the two potentials.

Cu²⁺(aq) + 2e⁻ → Cu(s) E°red = +0.339 V
Zn(s) → Zn²⁺(aq) + 2e⁻ E°ox = +0.762 V

Cu²⁺(aq) + Zn(s) → Cu(s) + Zn²⁺(aq) E°cell = +1.101 V