The Haber process — AQA GCSE Chemistry
Test yourself on The Haber process with AQA GCSE practice questions.
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The Haber process explained
In the Haber process, purified nitrogen and hydrogen are passed over an iron catalyst at about 450°C and about 200 atmospheres.
Read the full explanation
Some nitrogen and hydrogen react to form ammonia, but because the reaction is reversible, some ammonia breaks down again into nitrogen and hydrogen, so an equilibrium mixture leaves the reactor. The mixture is cooled; ammonia liquefies and is removed, while unreacted nitrogen and hydrogen remain as gases and are recycled back into the reactor. Recycling improves the overall yield because it gives unreacted gases further chances to react. The word equation is nitrogen + hydrogen ⇌ ammonia, and the balanced symbol equation is N₂ + 3H₂ ⇌ 2NH₃.
Your focus
- Describe the conditions and catalyst used in the Haber process.
- Explain how ammonia is separated and how unreacted gases are recycled.
- Write the word and balanced symbol equations for the Haber process using the reversible arrow.
The Haber process exam tips
Marking Points
- Purified nitrogen and hydrogen are passed over an iron catalyst.
- The temperature used is about 450°C.
- The pressure used is about 200 atmospheres.
- The reaction is reversible, so ammonia can break down into nitrogen and hydrogen.
- Cooling the mixture liquefies ammonia, which is then removed.
- Unreacted nitrogen and hydrogen are recycled back into the reactor.
- The word equation is nitrogen + hydrogen ⇌ ammonia.
- The balanced symbol equation is N₂ + 3H₂ ⇌ 2NH₃.
Examiner Tips
- 💡Quote the conditions as about 450°C and about 200 atmospheres, including the word 'about' because they are approximate.
- 💡Name iron as the catalyst and state that it speeds up the reaction without being used up.
- 💡When describing the process, use the sequence react, cool, liquefy, remove, recycle to keep your answer ordered.
Common Mistakes
- Writing the equation with a single arrow instead of the reversible arrow: the error is ignoring reversibility; the correction is to use ⇌ in the equation.
- Saying ammonia is removed by filtration: the error is choosing the wrong separation method; the correction is that ammonia is liquefied by cooling and then removed as a liquid.
- Forgetting to recycle unreacted gases: the error is treating the reactor as a one-pass complete reaction; the correction is that remaining nitrogen and hydrogen are returned to the reactor.