For the gaseous Haber synthesis: N₂(g) + 3H₂(g) <=> 2NH₃(g) (ΔH = -92 kJ/mol), which set of conditions favors the maximum equilibrium yield of ammonia according to Le Chatelier's principle?

Answer and explanation

Correct answer: A. high pressure and low temperature

  1. Step 1: Pressure: Forward reaction proceeds with a decrease in gaseous moles (4 mol reactants -> 2 mol products). Increasing pressure shifts equilibrium to the side with fewer gas moles (favors NH₃). Step 2. Temperature: Forward reaction is exothermic (ΔH < 0). Lowering temperature shifts equilibrium in the exothermic direction to generate heat (favors NH₃). Step 3. High pressure and low temperature maximize yield. Answer: high pressure and low temperature. Why not the others: Low pressure favors dissociation into N₂ and H₂; high temperature favors endothermic reverse reaction.

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