What is the maximum useful work which can be obtained from a hydrogen-oxygen fuel cell that produces 1.75 kg o

Question

What is the maximum useful work which can be obtained from a hydrogen-oxygen fuel cell that produces 1.75 kg of water at 25°C?

(Assume 1 atm pressure for the gases.)

Answer 1

The maximum possible work available from hydrogen-oxygen combustion is
2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ/mol
(1,750 g)(572 kJ/mol)(1 mol/18.016g) ≈
55,562 kJ

fuel cells are about 50% efficient, lowering the maximum useable work to 27,781 kJ. Further losses (transmission and conversion) are encountered in practice. In purely electrical applications with resistive loads, these losses will be on the order of 3%. For mechanical conversions needed for vehicles, one can expect a "tank-to-wheel" efficiencies from 36% to 45%, or 38,585 kJ to 48,231 kJ, according to Wikipedia.