The Haber Process

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Nitrogen and Hydrogen are needed to make Ammonia

- Temperature

- Pressure

N + 3H 2NH (+ heat)

- Higher pressure favours the forward reaction

- So the pressure is set as high as possible to give the best % yield without it being too expensive

- Forward reaction is exothermic - inc the temp will move the equilibrium away from ammonia, the yield of ammonia is greater at lower temperatures

- BUT, lower temperatures have a lower rate of reaction so they keep it high

- 450°C is a compromise between maximum yield and speed of reaction

(better to wait 20 seconds for 10% yield than 60 seconds for 20% yield)

- Ammonia is formed as a gas but as it cools in the condenser it is liquefied and is removed

- Unused hydrogen and nitrogen are recycled so nothing is wasted

- The iron catalyst speeds up the reaction so it gets to equilibrium proportions quicker

- Without it the temp would have to be raised further which would reduce the % yield

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