The thermochemical equation for the dissociation of hydrogen gas into atoms may be written as: H 2 → 2H; ΔH = 436 kJ. What is the ratio of the energy yield on combustion of 1 mole of hydrogen atoms to

Question

The thermochemical equation for the dissociation of hydrogen gas into atoms may be written as: H 2 → 2H; ΔH = 436 kJ. What is the ratio of the energy yield on combustion of 1 mole of hydrogen atoms to steam to the yield on combustion of 1 mole of hydrogen molecules to steam? Heat of formation of steam is -242 kJ/mol.

TestHub · Accepted Answer

1 mol H 2 burning to steam gives 242 kJ. 1 mol H atoms equals 1/2 mol H 2 , so the yield is 1/2(436 + 242) = 339 kJ (the atoms first combine to H 2 , releasing 218 kJ, then burn, releasing 121 kJ). Ratio = 339/242 = 1.40. This is option (a).

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