GCSE Chemistry · Edexcel 1CH0 · Topic 5C
Dynamic equilibria and the Haber process
Key points
- Higher tier: the Haber process (N₂ + 3H₂ ⇌ 2NH₃) is exothermic in the forward direction and has fewer gas molecules on the product side.
- High pressure increases the yield and the rate, but is costly and dangerous, so about 200 atm is used.
- Low temperature gives a higher yield but a slow rate, so a compromise of about 450 °C is used.
- An iron catalyst increases the rate without changing the yield. Unreacted gases are recycled.
- Fertilisers supply nitrogen, phosphorus and potassium (NPK). Ammonia is reacted with acids to make salts such as ammonium nitrate and ammonium sulfate.
- Industrial production is continuous from raw materials; lab preparation uses titration and crystallisation on a small scale.
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