The Haber Process
- Ammonia is manufactured using The Haber Process which occurs in five stages
- Stage 1: H2 and N2 are obtained from natural gas and the air respectively and are pumped into the compressor through pipe
- Stage 2: the gases are compressed to about 200 atmospheres inside the compressor
- Stage 3: the pressurised gases are pumped into a tank containing layers of catalytic iron beds at a temperature of 450°C. Some of the hydrogen and nitrogen react to form ammonia:
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
- Stage 4: unreacted H2 and N2 and product ammonia pass into a cooling tank. The ammonia is liquefied and removed to pressurised storage vessels
- Stage 5: the unreacted H2 and N2 gases are recycled back into the system and start over again
The production of ammonia by the Haber Process
Conditions
Temperature: 450ºC
- A higher temperature would favour the reverse reaction as it is endothermic (takes in heat) so a higher yield of reactants would be made
- If a lower temperature is used it favours the forward reaction as it is exothermic (releases heat) so a higher yield of products will be made
- However at a lower temperature the rate of reaction is very slow
- So 450ºC is a compromise temperature between having a lower yield of products but being made more quickly
- A lower pressure would favour the reverse reaction as the system will try to increase the pressure by creating more molecules (4 molecules of gaseous reactants) so a higher yield of reactants will be made
- A higher pressure would favour the forward reaction as it will try to decrease the pressure by creating less molecules (2 molecules of gaseous products) so a higher yield of products will be made
- However high pressures can be dangerous and very expensive equipment is needed
- So 200 atm is a compromise pressure between a lower yield of products being made safely and economically
Catalyst
- A catalyst of iron is used to speed up the reaction
Choosing the conditions for the Haber Process
Examiner Tip
The reaction conditions chosen for the Haber process are not ideal in terms of the yield but do provide balance between product yield, reaction rate and production cost. These are called compromise conditions as they are chosen to give a good compromise between the yield, rate and cost.
