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10.4.1The Haber process

AQA GCSE Chemistry (8462), Higher tier · Using resources › The Haber process and NPK fertilisers

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Balance the equation for the reaction.
N2 + ....H2 ⇌ ....NH3
N2 + 3H2 ⇌ 2NH3
State the formula of ammonia.
NH3

Sample questions

Written for this site in the style of AQA exam questions. They are not taken from real past papers.

Question 1Easy5 marks
Ammonia is manufactured by the Haber process.
(a) Give the source of the nitrogen used in the Haber process.[1]
(b) Give the source of the hydrogen used in the Haber process.[1]
(c) Which catalyst is used in the Haber process?
Tick (✓) one box.[1]
  • Iron
  • Nickel
  • Platinum
  • Vanadium(V) oxide
(d) Give the approximate temperature and pressure used in the Haber process.[2]
Show the answer and mark scheme
(a)
  • the air
(b)
  • natural gas / methane (reacted with steam)
(c) Answer: Iron
(d)
  • (about) 450 °C
  • (about) 200 atmospheres
Question 2Medium6 marks
In the Haber process, purified nitrogen and hydrogen are passed over a catalyst. Some of the nitrogen and hydrogen react to form ammonia.
(a) Balance the equation for the reaction.
N2 + ....H2 ⇌ ....NH3[1]
(b) What does the symbol ⇌ show about the reaction?[1]
(c) Describe how the ammonia is separated from the unreacted nitrogen and hydrogen.[2]
(d) What happens to the unreacted nitrogen and hydrogen?
Give a reason for your answer.[2]
Show the answer and mark scheme
(a) Answer: N2 + 3H2 ⇌ 2NH3
  • N2 + 3H2 ⇌ 2NH3
(b)
  • the reaction is reversible
(c)
  • the gases are cooled
  • the ammonia liquefies (and is removed) but nitrogen and hydrogen stay as gases
(d)
  • they are recycled (back into the reactor)
  • so raw materials are not wasted / more ammonia is made from them
Question 3Hard7 marks
The Haber process reaction is reversible. The forward reaction is exothermic.
N2(g) + 3H2(g) ⇌ 2NH3(g)
(a) Explain why a lower temperature would give a higher equilibrium yield of ammonia.[2]
(b) Explain why a temperature of about 450 °C is used rather than a lower temperature.[2]
(c) Explain the effect of the iron catalyst on the rate of reaction and on the yield of ammonia.[2]
(d) The reaction transfers energy to the surroundings.
Suggest how the manufacturer could use this energy.[1]
Show the answer and mark scheme
(a)
  • lowering the temperature shifts the position of equilibrium in the exothermic direction
  • which is the forward reaction, so more ammonia is formed
(b)
  • at lower temperatures the rate of reaction is (too) slow
  • 450 °C is a compromise that gives an acceptable yield in a short time
(c)
  • the catalyst increases the rate of both the forward and reverse reactions, so equilibrium is reached faster
  • it does not change the position of equilibrium / the yield
(d)
  • to heat the incoming gases / to produce steam (to generate electricity or drive compressors)

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