10.10 The Haber process
6 exam questions worth 12 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which catalyst is used in the Haber process?
Choose one answer.
Correct Not quite: the answer is Iron
Mark scheme
B
Model answer
B: an iron catalyst is used.
Give the sources of the nitrogen and the hydrogen used in the Haber process.
Mark scheme
- nitrogen: the air (1)
- hydrogen: natural gas / methane (1)
Model answer
Nitrogen comes from the air and hydrogen from natural gas.
Explain what happens to the nitrogen and hydrogen that do not react.
Mark scheme
- they are recycled back into the reactor (1)
Model answer
They are recycled into the reactor, so they are not wasted.
Higher tier.
Explain why a temperature of 450 °C is used in the Haber process.
Mark scheme
- forward reaction is exothermic (1)
- lower temperature gives a higher yield (1)
- but the rate would be too slow (1)
- 450 °C is a compromise between rate and yield (1)
Model answer
The forward reaction is exothermic, so a lower temperature would give a higher yield of ammonia. However, at low temperatures the reaction would be too slow. 450 °C is a compromise that gives an acceptable yield at a fast enough rate.
Higher tier.
Explain why a high pressure increases the yield of ammonia.
Mark scheme
- fewer molecules of gas on the right (2) than the left (4) (1)
- high pressure shifts the equilibrium to the side with fewer gas molecules (1)
Model answer
There are fewer gas molecules on the product side, so increasing the pressure shifts the equilibrium to the right, producing more ammonia.
Explain how the ammonia is separated from the unreacted gases.
Mark scheme
- the mixture is cooled (1)
- ammonia liquefies / condenses (and nitrogen and hydrogen stay as gases) (1)
Model answer
The mixture is cooled; ammonia condenses to a liquid, while nitrogen and hydrogen remain gases.
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