Haber Process for the Production of Ammonia

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Haber Process for the Production of Ammonia

During World War I Germans needed Nitrogen to produce explosive. Owing to the blockage of supply of ammonia, Germans were looking for methods of preparation of large-scale production of ammonia.  In 1909 Fritz Haber described the process by combining nitrogen and hydrogen. This process is called Heber Process. Later on Carl Bosch developed the Haber synthesis into an industrial process.

Raw Materials:

  • The raw materials for creating ammonia are air for nitrogen N2 (g) and methane and water for hydrogen H2 (g).

  • Methane CH4 (g) is reacted with steam H2O (g) to give carbon dioxide CO2 (g) and hydrogen H2 (g).

  • Carbon monoxide (CO) in the mixture is oxidised to CO2 using steam and an iron oxide catalyst:

  • The nitrogen N2 (g) is obtained from the air by fractional distillation, because the air is made up of 80% nitrogen.

The process

Following conditions are essential to combine nitrogen N2 (g) and hydrogen H2 (g).

  • Medium temperature (around 500oC)
  • Very high pressure (ranging from 200 atmospheres to 351kPa)
  • Use of a catalyst:
  • A porous iron catalyst prepared by reducing magnetite, Fe3O4).
  • Osmium is a much better catalyst for the reaction but is very expensive.

Characteristics of the process:

  • The reaction is a reversible one.
  • This process yield approximately 10-20% of ammonia, NH3 (g),
  • The reaction between nitrogen and hydrogen to produce ammonia is exothermic, releasing 92.4kJ/mol of energy at 298K (25oC).

OR

Explanation of Reactions:

  • Add N2 (g) - this will increase the reactant concentration. The system will therefore try to balance the equilibrium by making more product, in this case NH3 (g). If N2 (g) is removed the system will try to balance the equilibrium by making more reactant from products, therefore there will be less ammonia produced.

  • Add H2 (g) - this will increase the reactant concentration. The system will therefore try to balance the equilibrium by making more product, in this case NH3 (g). If H2 (g) is removed the system will try to balance the equilibrium by making more reactant from products, therefore, there will be less ammonia produced.

  • Add NH3 (g) - this will increase the product's concentration. The system will therefore try to balance the equilibrium by making more reactant, in this case N2 (g) and H2 (g). Even though part of the ammonia added is consumed to make reactants, it will still be higher than initial. If NH3 (g) is removed the system will try to balance the equilibrium by making more product from reactants, therefore there will be less H2 (g), N2 (g) and NH3 (g) produced.
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  • Decrease temperature - this will decrease kinetic energy. Energy is on the right side, so the system will shift to make energy. Since the reaction is exothermic, this will favour ammonia (right side) - more ammonia will be produced. If the temperature is increased, the system will shift away from energy and more reactants will be produced and less ammonia will be produced.

  • Increase pressure / decrease the volume - the system will shift to reduce pressure. Since less particles = less pressure and knowing that the reactant side has 4 particle and the product side has ...

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