Key Equation
- N₂ + 3H₂ ⇌ 2NH₃
- Forward reaction: exothermic
- Reversible (⇌)
Conditions
- ~450°C (compromise)
- ~200 atm (compromise)
- Iron catalyst
- Unreacted gases recycled
Raw Materials
- N₂ — from air
- H₂ — from natural gas (methane)
Uses and Key Logic
- Makes fertilisers (NPK)
- High P → more NH₃ but costly
- Low T → more NH₃ but slow
- Catalyst → faster rate, same yield
Common Mistakes
- Saying the catalyst increases yield: The iron catalyst only increases the rate — it does NOT shift the equilibrium position or change the yield
- Saying high temperature gives more ammonia: High temperature shifts equilibrium LEFT (away from the exothermic forward reaction) — lower temperature gives more ammonia but too slowly; 450°C is the compromise
- Forgetting where nitrogen and hydrogen come from: Nitrogen comes from fractional distillation of AIR; hydrogen comes from natural gas (methane/steam reforming)
- Saying unreacted gases are wasted: Unreacted N₂ and H₂ are recycled back into the reactor — nothing is wasted