Formation of Ammonia

Specification Point 4.15:
  • Describe the formation of ammonia as a reversible reaction between nitrogen (extracted from the air) and hydrogen (obtained from natural gas) and that it can reach a dynamic equilibrium
  • Ammonia is manufactured using The Haber Process which involves a reversible reaction between nitrogen and hydrogen:

N2(g) + 3H2(g) ⇌ 2NH3(g)

  • The nitrogen is extracted from the air by fractional distillation and the hydrogen is extracted from methane by reaction with steam under high pressure.
  • When only nitrogen and hydrogen are present at the beginning of the reaction, the rate of the forward reaction is at its fastest, since the concentrations of both reactants are at their highest.
  • As the reaction proceeds, the concentration of the reactant molecules (N2 and H2) gradually decreases so the rate of the forward reaction will decrease.
  • As the concentration of the product molecules (NH3) is gradually increasing, the rate of the reverse reaction increases as more and more of the NH3 molecules decompose to form H2 and N2.
  • Since the reaction is reversible and in a closed system, the rate of the forward reaction and the rate of the backward reaction will eventually become equal and dynamic equilibrium is reached where the molecules on the left and right of the equation are constantly chemically changing into each other.
  • This occurs extremely fast, hence the concentration of each is constant.

Dynamic Equilibrium with Catalyst, Edexcel GCSE Chemistry

Diagram showing when the rates of forward and backward reactions become equal

Conditions for the Haber Process

Specification Point 4.16:
  • Recall the conditions for the Haber process as:
    a) temperature 450 °C
    b) pressure 200 atmospheres
    c) iron catalyst
  • The Haber process occurs at specific conditions.
  • These are:
    • Temperature of 450ºC.
    • Pressure of 200 atmospheres (this is 200 times the normal atmospheric pressure at ground level!).
    • Iron beads are used which act as a catalyst.

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Edexcel GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.