Instead of burning zinc in oxygen to form ZnO and to obtain energy, one can cause the oxidation of zinc in air (oxygen) to occur in an electrochemical cell. In the process, one produces electricity.
(a) Without knowing the detailed electrochemical reactions, determine the standard electrode potential for such a zinc-air battery. The standard Gibbs free energy for the formation of ZnO is - 320 kJ/mole. The answer should be between 1.5 and 2.0 volts.
(b) Zinc is being consumed in this battery, while oxygen comes from outside the battery. Given that the atomic weight of Zn is 65.4 and F = 96500 Coulombs, show that the energy capacity of this battery is about 1360 watt-hr/kg of zinc.
(c) The energy capacity of actual zinc-air batteries is around 450 watt-hr/kg of the battery. Discuss two reasons for such discrepancy.