Ammonia has many important uses. It is manufactured industrially by the Haber Process. The raw materials for the Haber process are the nitrogen and hydrogen.



Nitrogen is obtained from the fractional distillation of liquid air.



Hydrogen is produced from the cracking of petroleum.



Conditions required for Manufacturing Ammonia:

The nitrogen molecule is generally unreactive. Hence, there is no reaction at all between nitrogen and hydrogen at room temperature and pressure. For nitrogen to react with hydrogen to form ammonia, a high pressure and a relatively high temperature are needed. Iron is used as catalyst to speed up the reaction. The equation for the Haber process is:


                         Nitrogen   + Hydrogen     →   Ammonia


Because the reaction is reversible, some of ammonia formed may decompose and convert back to nitrogen and hydrogen. To achieve the maximum yield of ammonia at minimum cost, the reaction conditions (pressure and temperature) are carefully controlled.



How is the optimal pressure for the manufacturing of ammonia is selected?

  • The higher the pressure, the higher the yield of ammonia.
  • High pressure also increases the speed of reaction.
  • However, maintaining a high pressure is costly because expensive equipment (like special pumps and stronger pipes) is required.
  • Therefore, there is a limit to the amount of pressure that can be applied

How is the optimal temperature for the manufacture of ammonia selected?

  • The lower the temperature, the higher the yield of ammonia.
  • This is because the decomposition of ammonia is reduced.
  • However, a lower temperature also results in a slower reaction.
  • Therefore, a relatively high temperature of 450 C is used.

Why is catalyst used?

  • Despite conditions like high pressure and temperature, the reaction is still slow.
  • Therefore, a catalyst is used to speed up the reaction.

How is ammonia manufactured by the Haber process?





Steps for the Haber process:

  1. Nitrogen and hydrogen are mixed in ratio 1: 3.
  2. The mixture of gases is compressed to 250 atm.
  3. The gases are heated to 450 C and passed over a finely divided iron. Iron acts as a catalyst in the reaction. The reaction is exothermic. Only about 10-15% of nitrogen and hydrogen is converted to ammonia.
  4. A mixture of ammonia, nitrogen and hydrogen is obtained. Mixture is cooled.
  5. Ammonia gas condenses to form liquid ammonia.