The zinc-air battery shows much promise for electric ears

Chapter 19, Problem 115AP

(choose chapter or problem)

The zinc-air battery shows much promise for electric cars because it is lightweight and rechargeable:

                                                         

The net transformation is \(\mathrm{Zn}(s)+\frac{1}{2} \mathrm{O}_2(\mathrm{~g}) \longrightarrow \mathrm{ZnO}(s)\).

(a) Write the half-reactions at the zinc-air electrodes, and calculate the standard emf of the battery at \(25^{\circ} \mathrm{C}\).

(b) Calculate the emf under actual operating conditions when the partial pressure of oxygen is 0.21 atm.

(c) What is the energy density (measured as the energy in kilojoules that can be obtained from \(1 \mathrm{~kg}\) of the metal) of the zinc electrode?

(d) If a current of \(2.1 \times 10^5 \mathrm{~A}\) is to be drawn from a zinc-air battery system, what volume of air (in liters) would need to be supplied to the battery every second? Assume that the temperature is \(25^{\circ} \mathrm{C}\) and the partial pressure of oxygen is 0.21 atm.