Ammonia is industrially synthesized according to the following balanced equation at 298K and 1atm:
N₂(g) + 3 H₂(g) → 2 NH₃(g)
The standard enthalpy of formation of NH₃(g) is −46.1kJ mol−1. The elements in their standard states have ΔHf∘=0kJ mol−1.
(a) Calculate the standard enthalpy change, ΔH∘, for the reaction as written. Show all work and include units.
(b) Express the enthalpy change on a per-mole-of-NH₃ basis, and state whether the synthesis of ammonia is exothermic or endothermic. Justify your classification using the calculated value.