AQA GCSE Chemistry Foundation (8462), Foundation tier · Using resources › The Haber process and NPK fertilisers
Practise The Haber process. 6 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How ammonia is manufactured from nitrogen and hydrogen, and the conditions used. This is in GCSE Chemistry only, not in Combined Science. Expect recall of the conditions.
Key facts
N2 + 3H2 ⇌ 2NH3 (forward reaction exothermic)
Nitrogen from the air; hydrogen from natural gas
Conditions: iron catalyst, about 450 °C, about 200 atmospheres
Cool → ammonia liquefies and is removed; unreacted N2 and H2 are recycled
Catalyst: faster rate
Ammonia is used to make nitrogen-based fertilisers
Notes
Making ammonia
The Haber process manufactures ammonia, NH3, which can be used to produce nitrogen-based fertilisers.
The raw materials are nitrogen, from the air, and hydrogen, from natural gas (methane).
nitrogen + hydrogen ⇌ ammonia, or N2 + 3H2 ⇌ 2NH3
The reaction is reversible, and the forward reaction is exothermic.
The process
diagram
The purified gases are passed over an iron catalyst at a high temperature (about 450 °C) and a high pressure (about 200 atmospheres).
Some of the nitrogen and hydrogen react to form ammonia. Because the reaction is reversible, some of the ammonia breaks down again into nitrogen and hydrogen.
The gas mixture is cooled: the ammonia liquefies and is removed (ammonia has a much higher boiling point than nitrogen and hydrogen).
The unreacted nitrogen and hydrogen are recycled back over the catalyst, so little is wasted.
N2 + 3H2 ⇌ 2NH3: ammonia is removed as a liquid; unreacted gases go round again.
How to answer each type of question
Recall the raw materials and conditions
1 to 4 marksGrade 4
Nitrogen from the air; hydrogen from natural gas.
Give the conditions with units: about 450 °C and about 200 atmospheres.
The catalyst is iron.
Example. (a) Give the source of the hydrogen used in the Haber process. (1 mark) (b) State the temperature and pressure used in the Haber process. (2 marks) (c) Name the catalyst. (1 mark)
Show the model answerHide the model answer
(a) Natural gas / methane (1) (b) About 450 °C (1); about 200 atmospheres (1) (c) Iron (1)
Describe what happens to the gases after the reactor
2 to 3 marksGrade 5
Say that the mixture is cooled.
Say that the ammonia liquefies and is removed.
Say that the unreacted nitrogen and hydrogen are recycled.
Example. The gas mixture leaving the reactor contains ammonia, nitrogen and hydrogen. Describe how the ammonia is separated from the mixture and what happens to the other gases. (3 marks)
Show the model answerHide the model answer
The mixture is cooled (1). The ammonia liquefies (condenses) and is removed (1). The unreacted nitrogen and hydrogen are recycled back over the catalyst (1).
Don’t lose marks
Saying the catalyst increases the yield. It only increases the rate.
Swapping the sources: nitrogen comes from the air and hydrogen from natural gas.
More tips
Memory tricks
The Haber numbers: iron, 450 °C, 200 atmospheres.
A catalyst changes how fast, never how much.
Exam technique
When a graph or table is given, quote values from it with units to support your answer.
Give the conditions with 'about': about 450 °C and about 200 atmospheres.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
State what the Haber process makesAmmonia, which is used to make nitrogen-based fertilisers.
Grade 4
Give the sources of nitrogen and hydrogenNitrogen comes from the air; hydrogen comes from natural gas (methane).
Grade 4
Recall the conditions usedAn iron catalyst, about 450 °C and about 200 atmospheres.
Grade 5
Describe how ammonia is separated and gases recycledOn cooling, ammonia liquefies and is removed; unreacted nitrogen and hydrogen are recycled.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Balance the equation for the reaction. N2 + ....H2 ⇌ ....NH3
N2 + 3H2 ⇌ 2NH3
State the formula of ammonia.
NH3
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Ammonia is manufactured by the Haber process.
(a) Give the source of the nitrogen used in the Haber process.[1]
(b) Give the source of the hydrogen used in the Haber process.[1]
(c) Which catalyst is used in the Haber process? Tick (✓) one box.[1]
Iron
Nickel
Platinum
Vanadium(V) oxide
(d) Give the approximate temperature and pressure used in the Haber process.[2]
Show the answer and mark scheme
(a)
the air
(b)
natural gas / methane (reacted with steam)
(c)Answer: Iron
(d)
(about) 450 °C
(about) 200 atmospheres
Question 2Medium6 marks
In the Haber process, purified nitrogen and hydrogen are passed over a catalyst. Some of the nitrogen and hydrogen react to form ammonia.
(a) Balance the equation for the reaction. N2 + ....H2 ⇌ ....NH3[1]
(b) What does the symbol ⇌ show about the reaction?[1]
(c) Describe how the ammonia is separated from the unreacted nitrogen and hydrogen.[2]
(d) What happens to the unreacted nitrogen and hydrogen? Give a reason for your answer.[2]
Show the answer and mark scheme
(a)Answer: N2 + 3H2 ⇌ 2NH3
N2 + 3H2 ⇌ 2NH3
(b)
the reaction is reversible
(c)
the gases are cooled
the ammonia liquefies (and is removed) but nitrogen and hydrogen stay as gases
(d)
they are recycled (back into the reactor)
so raw materials are not wasted / more ammonia is made from them