Haber & Ostwald Processes (SQA National 5 Chemistry): Revision Note

The Haber process

• The Haber process is an industrial process

• It is used to manufacture the ammonia (NH₃) required for fertiliser production

The reaction

• The process is a reversible reaction between nitrogen gas (from the air) and hydrogen gas:

nitrogen + hydrogen ⇌ ammonia

N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)

• The ⇌ symbol shows that the reaction is reversible

  • This means that the reaction can go in both directions

  • The forward direction makes ammonia

  • The backward direction breaks ammonia down

The conditions

• Choosing the right conditions for the Haber process involves a compromise between:

  • The rate / speed of the reaction

  • The amount of product you get (the yield)

Temperature

• At low temperatures:

  • The forward reaction is favoured

  • This gives a high yield of ammonia

  • However, the reaction is too slow to be economical

• At high temperatures:

  • The rate of reaction increases

    • This is because particles have more energy, leading to more frequent and successful collisions

  • However, the backward reaction becomes more dominant

  • This leads to a low yield of ammonia

• This means that a compromise temperature is used to get a reasonable rate and a reasonable yield

Catalyst

• An iron catalyst is used to increase the rate of reaction

• The catalyst speeds up both the forward and backward reactions equally

• This allows the process to become fast enough to be economical at the compromise temperature

The Ostwald process

• The Ostwald process is the industrial method for producing the nitric acid (HNO₃) needed to make fertilisers

The reaction

• Ammonia, made in the Haber process, is the essential starting material

• In the Ostwald process:

  • Ammonia reacts with oxygen (from the air)

  • Water is also used in the process

  • The final product is nitric acid

The catalyst

• A platinum catalyst is used to speed up the reaction between ammonia and oxygen

• Like all catalysts, the platinum is not used up and can be recovered at the end of the reaction

Linking the processes

• The Haber and Ostwald processes are linked together in the production of ammonium nitrate, a key fertiliser

• The Haber process produces ammonia

• The Ostwald process uses some of the ammonia to produce nitric acid

• Ammonia (from the Haber process) and nitric acid (from the Ostwald process) are used to make ammonium nitrate