1. 1
   An engineer is setting up a plant to manufacture ammonia from nitrogen and hydrogen gas: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). The plant uses an iron catalyst and operates at approximately 450°C and approximately 200 atmospheres pressure.

   (a)

   Which raw material provides the nitrogen used in this process?

   [1 mark]

   • AThe air
   • BNatural gas
   • CLimestone
   • DSea water

   (b)

   What is the role of the iron in this process?

   [1 mark]

   • AIt is a reactant that is used up
   • BIt is a catalyst that increases the rate of reaction
   • CIt removes impurities from the nitrogen
   • DIt absorbs the ammonia produced

   (c)

   State the source of the hydrogen used in this process and explain why an iron catalyst is used.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a Haber process plant, the gas mixture leaving the reaction chamber contains ammonia together with unreacted nitrogen and hydrogen, since the reaction does not go to completion. This mixture is cooled, and the unreacted gases are recycled back into the reaction chamber.

   (a)

   After the gas mixture leaves the reaction chamber, it is cooled. What happens to the ammonia as a result?

   [1 mark]

   • AIt decomposes back into nitrogen and hydrogen
   • BIt remains a gas and mixes further with the unreacted gases
   • CIt reacts further with the iron catalyst
   • DIt liquefies and can be separated from the unreacted gases

   (b)

   Why are the unreacted nitrogen and hydrogen gases recycled back into the reaction chamber rather than discarded?

   [1 mark]

   • ATo increase the temperature of the reaction chamber
   • BTo remove the iron catalyst from the system
   • CTo reduce wastage of raw materials and increase overall ammonia production
   • DTo convert the ammonia back into nitrogen and hydrogen

   (c)

   Explain why the reaction does not go to completion, and describe how the plant deals with this to maximise the overall production of ammonia.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farming cooperative relies on a nearby Haber process plant for the ammonia used to make its nitrogen fertilisers. The plant operates at approximately 450°C and 200 atmospheres, using an iron catalyst, and managers are reviewing whether these conditions are the best choice.

   (a)

   Explain, using ideas about equilibrium, why using a very high pressure such as 200 atmospheres increases the yield of ammonia in this reaction.

   [3 marks]

   (b)

   Explain why the plant uses a temperature of approximately 450°C rather than a much lower temperature, even though the forward reaction is exothermic and a lower temperature would give a higher equilibrium yield of ammonia.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An agricultural science class is discussing why the Haber process is considered one of the most important industrial chemical processes ever developed, given its role in producing fertilisers used across the world.

   (a)

   Discuss the global importance of the Haber process for producing fertilisers, and explain why nitrogen-based fertilisers are needed by farmers worldwide.

   [6 marks]

   (b)

   Evaluate the choice of approximately 450°C and 200 atmospheres as the operating conditions for the Haber process, considering the effects on rate, yield, cost and safety.

   [6 marks]

   Total for question 4: 12 marks

End of questions