The Haber process is a reversible reaction used to produce ammonia. The reaction can reach dynamic equilibrium. Describe what is meant by a reversible reaction and explain what would happen to the concentrations of nitrogen, hydrogen and ammonia once dynamic equilibrium is reached if the temperature is then increased.

Edexcel GCSE Chemistry (1CH0) — 4.2 Reversible reactions and equilibria · Describe and Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

In the Haber process, nitrogen and hydrogen react to produce ammonia. The forward reaction is exothermic.

Model answer (4 marks)

A reversible reaction is one in which the products can react together to reform the reactants.

Increasing the temperature favours the endothermic (reverse) reaction, so the concentration of ammonia decreases while the concentrations of nitrogen and hydrogen increase.

Examiner tips

  • Use the definition of a reversible reaction verbatim. Show the Le Chatelier principle: endothermic reverse reaction is favoured by heat. State the direction of change for each species clearly.
  • Use the exact wording from the mark scheme to secure full marks.

Common mistakes

  • Confusing the forward reaction as exothermic with the reverse as endothermic. Failing to mention that ammonia concentration falls. Using vague terms like "more of" instead of "increase" or "decrease".

Mark scheme (4 marks)

  1. A reversible reaction is one in which the products can react together to reform the reactants
  2. Increasing temperature favours the endothermic (backward/reverse) reaction
  3. The concentration of ammonia decreases
  4. The concentrations of nitrogen and hydrogen increase

Key terms in this question

reversible reaction · dynamic equilibrium · Haber process

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