Question

A galvanic cell cannot generate electricty forever. List two chemical reactions you can think of or why a galvanic cell may go “dead”.

Answer 1

The famous Nickel-Cadmium battery:

Ni2+ + 2 e− ⇌ Ni(s) −0.25

Cd2+ + 2 e− ⇌ Cd(s) −0.40

In which Nickel gets reduced, i.e. forms solid nickel metal while

Cadmium forms Cd2+ in solution

The electron flow will generate approx = 0.15 V each cell...

It goes "dead" since vnetually, all cadmium will turn to solution, i.e. solid Cd is not infinite.

In car batterries:

we use "acid lead" battery, there is content of H2SO4, sulfuric acid and lead

Pb(s) + HSO− 4(aq) → PbSO 4(s) + H+ (aq) + 2e−

PbO 2(s) + HSO− 4(aq) + 3H+ (aq) + 2e− → PbSO 4(s) + 2H 2O(l)

The battery will go "dead" typically when the Pb(s) + PbO2(s) form PbSO4(s) completely

This is common, that is why many times when we let lights on, there is no more "battery"