Question

Calculate delta H rxn (at 500K) for the formation of 1 mol of ammonia gas. (show worked out solution)

Answer 1

Nitrogen gas (N₂) and hydrogen gas (H₂) can be made to combine to form NH₃, or ammonia gas.

The reaction is N₂ + 3H₂ 2NH₃

This equation says that one mole of N₂ requires three moles of H₂ for a complete reaction, and this would then yield two moles of NH₃.

Nitrogen	+	Hydrogen		Ammonia
N2	+	3H2		2NH3
	+	3 H-H		2NH3
1 mole of N2	+	3 moles of H2		2 moles of ammonia
28 g of N	+	6 g of H		34 g ammonia

H= -92.4 KJ/mol

92.4kJ of energy is released for every one mole of N2

92.4kJ of energy is released for every three moles of H2

92.4kJ of energy is released for every two moles of NH3 produced.

Hence one mole of NH3 produces 92.4/2 = 46.0 kJ/mol energy

H = m*c*T

where m is mass of reactant

c is specific heat of product &

T is temperature

H = 0.02kg*6.74kJ/kgK*500

=67.4kJ/mol