Galvanic Cell Animation and Theory

made by Jelena Simovic Rota for the Physical Chemistry Department, University of Applied Sciences, Munich

A galvanic cell, also known as voltaic cell, is an electrochemical cell that generates electrical energy through a spontaneous reaction taking place in the cell. It consists of two half cells connected via external electrical circuit and via salt bridge.

A half cell contains a metal strip submerged into a solution of the metal's salt. Our example shows zinc-zinc chloride half cell (zinc electrode) and copper-copper sulfate half cell (copper electrode).

Two half cells are connected through a flow of electrons from zinc to copper electrode (external electrical circuit) and through a flow of ions (salt bridge).

The oxidation of Zn(s) into Zn2+ and the reduction of Cu2+ into Cu(s) occur spontaneously due to a difference in the potential energy between Zn and Cu2+. The oxidation takes place at the zinc anode and reduction takes place at the copper cathode.

Oxidation: Zn(s) → Zn2+ + 2e-

Reduction: Cu2+ + 2e- → Cu(s)

Electrons that are released at the zinc anode flow through the external electrical circuit towards the copper cathode.

A salt bridge is required to maintain electrical neutrality and allow the reaction to continue. Our salt bridge containing KNO3 is adding NO3- into the anode solution and K+ into the cathode solution in order to prevent charge build up.

The potential difference between two electrodes is called standard cell potential (Eocell) under standard state conditions: concentrations of 1 M, pressure of 1 atmosphere and temperature of 25 oC. It can be calculated using standard electrode potential, Eo, in volts, for each of the two half reactions:

Eocell = Eocathode - Eoanode

For our example:

Eocell = 0.337 V - (-0.763 V) = 1.100 V

In a galvanic cell, where a spontaneous reaction takes place, Gibbs free energy ∆G is negative and cell potential is positive, which is in accordance with the following equation:

∆G = −nFEcell

where n is the number of moles of electrons and F is the Faraday constant (96485 C/mol).