Question

Hydrogen gas is a very environmentally friendly fuel source. One factor that is important in determining whether it is used as a fuel source is the cost of production. Use the two equations below to evaluate which reaction requires more energy to produce 1 mol of ​H2(g). Reaction (1) as written produces ​H2(g) from methane and is 80.5% efficient. The production of ​ H2(g) by electrolysis of water, as shown in reaction (2), is 49.1% efficient.

(1) CH4 (g) + ​H2 O(l) → 3H2 (g) + CO(g) ∆H° r = +205.9 kJ
(2) ​H2O(l) → ​H2 (g) + ​ _1 2 O2 (g) ∆H° r = +285.8 kJ

Answer 1

So 205.9 kJ is needed to produce 3; 205.9/3 kJ will be needed to produce 1 mol and since that rxn is only 80.5% efficient then 205.9/3/0.805 will be needed to produce 1 mol at that level of efficiency. Do the same for the H2O electrolysis and compare.