A fertilizer manufacturer is comparing two routes for producing gaseous ammonia at 298 K.
Route A (direct): N2(g) + 3 H2(g) → 2 NH3(g)
Route B (two-step):
Step 1 N2(g) + O2(g) → 2 NO(g)
Step 2 2 NO(g) + 3 H2(g) → 2 NH3(g) + H2O(g)
Relevant ΔHf∘ data are given below.
Species ΔHf∘ (kJ·mol⁻¹)
N2(g) 0.0
H2(g) 0.0
O2(g) 0.0
NO(g) +90.3
NH3(g) −45.9
H2O(g) −241.8
(a) Determine the standard enthalpy change, ΔHrxn∘, for Route A.
(b) Determine ΔHrxn∘ for each step in Route B and for Route B overall.
(c) Based on your calculations, identify which route is thermodynamically more favorable at 298 K. Support your answer with quantitative evidence.
(d) Despite the enthalpy difference, Route B is not used industrially. Give ONE kinetic or operational reason that explains why the less favorable pathway might still be impractical.