Question

The enthalpy change for reaction N2 + 3H2(g) 2NH3(g) is 92.2kJ. The enthalpy of formation of ammonia is


a. –92.2 kJ
b. –46.1 kJ
c. –46.1 kJ/mol
d. –92.2 kJ/mol
e. cannot be determined

Answer 1

Answer: c. −46.1 kJ/mol.

Reason: The given reaction forms 2 mol NH3 with ΔH = −92.2 kJ (formation of NH3 is exothermic), so per mole ΔHf = −92.2 kJ / 2 = −46.1 kJ/mol.