Question 1 Medium
How is ammonia separated from the unreacted gases?
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Answer: by cooling it
- Ammonia has a higher boiling point than nitrogen and hydrogen.
- Cooling makes the ammonia condense to a liquid.
The Haber process and fertilisers: GCSE Combined Science Chemistry practice questions
A second set of questions on the Haber process and fertilisers. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
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Question 2 Medium
What symbol shows that the reaction is reversible?
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Answer: ⇌
- A reversible reaction has arrows both ways.
- The symbol is ⇌.
Question 3 Hard
Does the iron catalyst change the position of equilibrium?
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Answer: no
- A catalyst speeds up both forward and backward reactions equally.
- So it does not change the position of equilibrium.
Question 4 Hard
The forward reaction is exothermic. What happens to the yield of ammonia at equilibrium if the temperature is raised?
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Answer: it decreases
- Raising the temperature favours the endothermic direction.
- The backward reaction is endothermic, so less ammonia is made.
Question 5 Hard
In N₂ + 3H₂ ⇌ 2NH₃, how many molecules of gas are on the left-hand side?
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Answer: 4
- Add the numbers in front of the left-hand formulae.
- 1 + 3 = 4.
Question 6 Hard
Why is a pressure much higher than 200 atmospheres not used?
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Answer: it is too expensive
- High pressure needs strong pipes and powerful pumps.
- These are expensive and dangerous.
Question 7 Hard
Calculate the mass of ammonia (NH₃) made from 28 g of nitrogen (N₂). Ar: N = 14, H = 1. Give your answer in g.
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Answer: 34 g
- 28 g of N₂ is 1 mol.
- 1 mol of N₂ makes 2 mol of NH₃, which is 2 × 17 = 34 g.
Question 8 Hard
A plant should make 50 tonnes of ammonia but makes 12 tonnes. Calculate the percentage yield.
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Answer: 24%
- Percentage yield = actual ÷ maximum × 100.
- 12 ÷ 50 × 100 = 24%.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is the Haber process used to make?
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Ammonia.
Check 2
What is the balanced equation for the Haber process?
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N₂ + 3H₂ ⇌ 2NH₃.
Check 3
Where does the nitrogen come from?
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The air.
Check 4
Where does the hydrogen come from?
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Natural gas (methane).
Check 5
What temperature is used in the Haber process?
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About 450 °C.
Check 6
What pressure is used in the Haber process?
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About 200 atmospheres.
Check 7
What catalyst is used in the Haber process?
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Iron.
Check 8
What does the catalyst do?
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Speeds up the reaction. It does not change the yield.
Check 9
Is the forward reaction in the Haber process exothermic or endothermic?
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Exothermic.
Check 10
Why is a lower temperature not used?
Show answer
The reaction would be too slow.
Check 11
Why is a higher temperature not used?
Show answer
It would lower the yield of ammonia.
Check 12
Why does a high pressure increase the yield?
Show answer
There are fewer gas molecules on the right (2) than on the left (4).
Check 13
Why is a much higher pressure not used?
Show answer
Equipment is expensive and dangerous at very high pressure.
Check 14
How is ammonia separated from the unreacted gases?
Show answer
It is cooled and condenses to a liquid.
Check 15
What happens to unreacted nitrogen and hydrogen?
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They are recycled into the reactor.
Check 16
What is the formula of ammonia?
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NH₃.
Check 17
What is ammonia used to make?
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Fertilisers, such as ammonium nitrate.
Check 18
Why do farmers use fertilisers?
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They supply nitrogen, which plants need to grow, so crop yields rise.
Check 19
Why is too much fertiliser a problem?
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It can wash into rivers and harm wildlife.
Check 20
What ratio of nitrogen to hydrogen is used?
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1 : 3.
Check 21
What does dynamic equilibrium mean?
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Forward and backward reactions occur at the same rate, so amounts stay constant.
Check 22
What do NPK fertilisers contain? (Separate Chemistry only)
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Compounds of nitrogen, phosphorus and potassium.
Check 23
How is nitrogen separated from the air?
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By fractional distillation of liquid air.
Check 24
Does a catalyst change the position of equilibrium?
Show answer
No.
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