Question

Calculate ΔH∘ in kilojoules for the reaction of ammonia (ΔH∘f=−46.1 kJ/mol) with O2 to yield nitric oxide NO (ΔH∘f=91.3 kJ/mol) and H2O(g) (ΔH∘f=−241.8 kJ/mol), a step in the Ostwald process for the commercial production of nitric acid.,

Answer 1

1/2 N2 + 3/2 H2 -> NH3 : dH = -46.1 kJ/mol
1/2 N2 + 1/2 O2 -> NO : dH = +91.3 kJ/mol
H2 + 1/2 O2 -> H2O : : dH = -241.8 kJ/mol

The equation for the oxidation of ammonia to nitric oxide is

4 NH3 + 5 O2 -> 4 NO + 6 H2O

The heat of reaction is:

- 4 x -46.9 + 4 x 91.3 - 6 x 241.8 = -809kj