what energy change is associated with the reaction to obtain one mole of h2 from one mole of water vapor? the balanced equation is 2 h2o(g) → 2 h2(g) + o2(g) and the relevant bond energies are h h : 436 kj/mol; h o : 467 kj/mol; o o : 146 kj/mol; o o : 498 kj/mol.