Explaining the Haber Process (OCR GCSE Chemistry A (Gateway))

Explaining the Haber Process

Higher Tier Only

• The Haber Process produces ammonia from nitrogen and hydrogen:

N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)

• The conditions used are:

  • a pressure of 200 atmosphere

  • a temperature of 450 ^oC 

  • an iron catalyst 

• These conditions produce an equilibrium yield of ammonia of about 30% which seems low, however it is a balance between achieving a good yield of ammonia in a reasonable amount of time

Explaining the Conditions 

• Pressure

  • A pressure of 200 atmosphere is used as a compromise

  • High pressures would shift the equilibrium to the right due to there being less molecules on the right hand side of the equation resulting in a higher yield 

  • Very high pressures are hazardous and expensive so a lower pressure is used to reduce the risk

• Temperature

  • A temperature of 450^oC  is used as a compromise

  • The forward reaction is exothermic so a low temperature would shift the equilibrium to the right increasing the yield of ammonia

  • Low temperatures, however, result in a slower rate of reaction

  • The higher temperature allows ammonia to be made within a reasonable time frame 

The equilibrirum yield of ammonia at different pressures and temperatures

• Sometimes, there are a multiple methods for producing the same substance

• In cases like this, manufacturers have to consider the raw materials used and the amount of energy required for the process