Haber process- Additional science

Ammonia - A raw material which is used in the manufacture of fertilisers, explosives and cleaning fluids.

Fertilisers in plants - Plants cannot use nitrogen directly from the air, they can only use nitrogen molecules which have been dissolved in water so this allows them absorb nitrogen through roots.

- Ammonia is produced using a reaction between Nitrogen and Hydrogen by using the HABER PROCESS. The haber process is essential for plants to feed our population.

- The production of Ammonia is reversible

Nitrogen + Hydrogen <---> Ammonia

    N2      +     3H2      <--->    2NH3

Nitrogen  +  Hydrogen <----> Ammonia

The nitrogen in the haber process is obtained from the air. The hydrogen is obtained by cracking oil fractions or from natural gas.

As the production of ammonia is reversible, when nitrogen and hydrogen react to form ammonia, the ammonia is continually breaking up to form nitrogen and hydrogen.

The reacted ammonia is extracted and the remaining is recycled.

The two gasses, ammonia and hydrogen, are passed along an iron catalyst at high pressure, around 450C. If the temperature is increased, the balance shifts towards the left (as if it's trying to cool itself down) and the percentage yield of ammonia is decreased.

N₂ + 3H₂        2NH₃

There are four molecules of gas on the left hand side of the equation but only two on the right. If the pressure is increased, the balance shifts towards the right making fewer molecules (as if it's trying to reduce the pressure). So a high pressure gives a high percentage yield of ammonia.

The reaction is:

Exothermic from left to right

Endothermic from right to left

Increasing the temperature gives a higher rate of reaction so compromise have to be made.

• Price of energy: e.g. gas or electricity
• Cost of starting materials
• Equipment: E.g. Plant- expensive to build and maintain
• Catalyst - speeds up reaction but does not affect the % yield of ammonia.
• Labour costs: Wages etc.

The conditions used are all compromises.