Answer:
a) -243 kJ·mol⁻¹; b) -318.02 kJ·mol⁻¹
Step-by-step explanation:
The enthalpy of combustion is the energy released when one mole of a substance reacts completely with oxygen to form the oxides of its elements.
a) Combustion of hydrogen
2H₂(g) + O₂(g) ⟶ 2H₂O(g); kJ; ΔH° = -486 kJ
Δ_cH° = 1 mol H₂ × (-486 kJ/2 mol H₂) = -243 kJ·mol⁻¹
b) Combustion of ammonia
4NH₃(g) + 7O₂(g) ⟶ 4NO₂(g) + 6H₂O(g)
Δ_cH° = 1 mol NH₃ × (-1272.1 kJ/4 mol NH₃) = -318.02 kJ·mol⁻¹
