1. 1
   A chemical company operates a reversible gas-phase industrial reaction: A(g) + B(g) ⇌ C(g). The forward reaction is exothermic and produces fewer molecules of gas than the reactants. Engineers must choose a temperature and pressure that balance the rate of reaction against the equilibrium yield of C.

   (a)

   Which single change would increase the rate at which this reaction reaches equilibrium?

   [1 mark]

   • ALowering the temperature
   • BLowering the pressure
   • CRaising the temperature
   • DRemoving the catalyst

   (b)

   Which single change would increase the equilibrium yield of C?

   [1 mark]

   • ARaising the temperature
   • BRaising the pressure
   • CLowering the pressure
   • DAdding a catalyst

   (c)

   Explain why the engineers choose a compromise temperature rather than the lowest possible temperature, even though a lower temperature would give a higher equilibrium yield of C.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A different reversible industrial process produces a liquid product from two gaseous reactants: D(g) + E(g) ⇌ F(l). The forward reaction is endothermic. Engineers are testing how changes in temperature and pressure affect the position of equilibrium and the rate at which it is reached.

   (a)

   Which single change would increase the rate at which equilibrium is reached in this reaction?

   [1 mark]

   • ADecreasing the temperature
   • BRemoving the catalyst
   • CDecreasing the pressure
   • DIncreasing the temperature

   (b)

   Which single change would increase the equilibrium yield of F?

   [1 mark]

   • AIncreasing the pressure
   • BAdding a catalyst
   • CDecreasing the pressure
   • DDecreasing the temperature

   (c)

   Explain why the engineers do not simply use an extremely high pressure to maximise the yield of F.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student reads that an industrial reversible reaction between gases G and H forms gas J, where the forward reaction is exothermic and produces the same total number of gas molecules as the reactants. The industrial plant runs at 200°C and 100 atmospheres pressure using a solid catalyst.

   (a)

   Explain the effect that increasing pressure would have on the position of equilibrium in this reaction, given that the number of gas molecules is unchanged by the reaction.

   [3 marks]

   (b)

   Using ideas about rate and equilibrium yield, explain why the plant is operated at 200°C rather than at a much lower or much higher temperature.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A fertiliser manufacturer is designing a new plant for a reversible gas reaction, K(g) + 3L(g) ⇌ 2M(g), which is exothermic in the forward direction. They must decide on operating temperature, pressure and catalyst use, balancing profit against safety.

   (a)

   Discuss, using ideas about rate of reaction and equilibrium position, how the manufacturer should choose an operating temperature for this process. Your answer should cover the effect of temperature on both rate and yield, and explain why a compromise temperature is chosen.

   [6 marks]

   (b)

   Discuss, using ideas about rate of reaction and equilibrium position, how the manufacturer should choose an operating pressure for this process, including consideration of cost and safety, and explain why a catalyst may be used instead of relying on more extreme temperature or pressure.

   [6 marks]

   Total for question 4: 12 marks

End of questions