Haber process and fertilisers extra: GCSE Chemistry
Haber conditions as a compromise, NPK fertilisers and phosphate rock
The short version
N2 + 3H2 ⇌ 2NH3 at ~450 °C, 200 atm, iron catalyst. Ammonia is turned into fertilisers; phosphate rock is treated with acid.
Key idea
Forward reaction is exothermic. Recycle unreacted N2 and H2
Grade 2–3: Air nitrogen plus hydrogen becomes ammonia, with iron to speed it up, in a hot high-pressure plant.
Grade 5–6: I can write the equation and quote 200 atm, 450 °C, iron.
Grade 9: I name the sources, say the forward change is exothermic, and I mention recycling unreacted gases.
Go a bit deeper
high T: faster but lower yield (forward exo). 450 °C and 200 atm are the compromise
Grade 2–3: High pressure helps make more ammonia. The plant is not run extra-hot because then you would get less ammonia, even though it would be quicker.
Grade 5–6: I can say 4 moles to 2 moles, and forward exo so high T lowers yield.
Grade 9: I write a full compromise: rate vs yield vs cost/safety, and I never say the catalyst changes the yield at equilibrium.
Worked example
Worked example
Grade 2–3: Air nitrogen plus hydrogen becomes ammonia, with iron to speed it up, in a hot high-pressure plant. Grade 5–6: I can write the equation and quote 200 atm, 450 °C, iron. Grade 9: I name the sources, say the forward change is exothermic, and I mention recycling unreacted gases.
Lessons in this topic
- The Haber process
- Choosing the conditions
- From ammonia to fertilisers
- Phosphate rock
- Evaluating fertilisers
In the app each lesson is video (when we have a real YouTube id) then intro, learn and summary steps.
What the examiner wants
Explain the Haber compromise using rate and position of equilibrium, and describe how NPK fertilisers are made.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
The Haber equation is
The Haber catalyst is
Typical Haber conditions are about
A low temperature would
Common mistakes
- The Haber process is not a fuel cell and not biogas. It is ammonia manufacture. Do not write that the iron is used up.
- Do not say a higher temperature is used to increase yield. It is used so the rate is fast enough. Yield of ammonia falls as temperature rises.
- Ammonia is not spread on fields as a Haber-tower gas and left at that. The spec fertilisers are ammonium salts (and related compounds). Do not mix this with mycoprotein or compost.
- Phosphate rock is not a product of N2 + 3H2. Do not treat it as an ammonium salt. Acid makes it soluble.
Answers and working
Frequently asked questions
Is GCSE Haber process and fertilisers extra on Combined Science and Triple?
Haber process and fertilisers extra is Triple-only Chemistry. Combined Science students can skip it.
Which exam board is this Haber process and fertilisers extra page for?
The ideas are board-agnostic for AQA, Edexcel, OCR, WJEC and CCEA. Paper lengths and question numbers differ — check your specification.
Is Haber process and fertilisers extra Foundation or Higher?
The core ideas appear on both tiers. Higher papers add extra application and some HT-only detail, marked in lessons with a Higher badge.
Learn, try, get feedback, fix the mistake
Open the stepped lesson, then the quiz with hints. Required-practical and calculation questions use the same method you will need in the paper.
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