The Haber process
Makes ammonia , NH 3 \text{NH}_3 NH 3 fertilisers
Raw materials: nitrogen from the air and hydrogen from natural gas
(methane) reacted with steam
The purified gases are passed over an iron catalyst at about
450 °C and about 200 atmospheres
N 2 (g) + 3 H 2 (g) ⇌ 2 NH 3 (g) \text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)} N 2 (g) + 3 H 2 (g) ⇌ 2 NH 3 (g)
The reaction is reversible , so some ammonia breaks down again. On
cooling , the ammonia liquefies and is removed; the unreacted
nitrogen and hydrogen are recycled back into the reactor
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The Haber process N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g) the forward reaction is exothermic nitrogen from the air hydrogen from natural gas compressor reactor iron catalyst 450 °C 200 atmospheres cooled liquid ammonia run off ammonia has a higher boiling point, so it condenses first and is removed unreacted nitrogen and hydrogen are recycled Only about 15% of the gases react each time round, so recycling is what makes the process worthwhile. The conditions are a compromise. A lower temperature would give a higher yield, because the forward reaction is exothermic — but the reaction would be far too slow, so 450 °C is used instead. A higher pressure would give a higher yield too, because there are fewer gas molecules on the right — but very high pressures are dangerous and expensive. Ammonia is used to make fertilisers. Flow diagram of the Haber process: nitrogen and hydrogen in, compressor, reactor with iron catalyst at 450 °C and 200 atm, cooler where ammonia condenses and is drawn off, unreacted gases recycled
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In the full topic
• The Haber process• Choosing the conditions [Higher Tier]• NPK fertilisersRead the free chemistry topics →