Making ammonia and sulfuric acid Cambridge IGCSE Chemistry revision
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In plain words
Two of the most important chemicals in the world are made by reversible reactions: ammonia (for fertilisers) by the Haber process, and sulfuric acid by the Contact process. In both, the conditions are a compromise between getting a lot of product and getting it quickly.
Three things to know
- Haber process: N₂ + 3H₂ ⇌ 2NH₃, at 450 °C and 20 000 kPa (200 atmospheres), with an iron catalyst. The nitrogen comes from the air and the hydrogen from methane (natural gas).
- Contact process: 2SO₂ + O₂ ⇌ 2SO₃, at 450 °C and 200 kPa (2 atmospheres), with a vanadium(V) oxide catalyst. Sulfur dioxide comes from burning sulfur or roasting sulfide ores; the oxygen comes from the air.
- A lower temperature would give more product but far too slowly, so 450 °C is a compromise. Very high pressures give more ammonia but cost more and are less safe.
Tips and tricks
- Learn the two sets of conditions as a table: temperature, pressure, catalyst. The temperature is the same for both.
- "Compromise" is the word examiners want for the temperature: a reasonable yield at a reasonable rate.
It lands in your notebook with its questions as flashcards.
Making ammonia and sulfuric acid: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which two gases react in the Haber process?
N₂ + 3H₂ ⇌ 2NH₃.
What is the catalyst in the Haber process?
Iron is cheap and works well.
Where does the nitrogen for the Haber process come from?
Air is about 78% nitrogen.
What is the catalyst in the Contact process?
It speeds up the reaction of sulfur dioxide with oxygen.
Why is the Haber process not run at a very low temperature, which would give a higher yield?
450 °C gives a reasonable yield reasonably quickly.
What is made in the reversible step of the Contact process?
2SO₂ + O₂ ⇌ 2SO₃. It is then turned into sulfuric acid.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 10 marks. Write your answers on paper, then check them.
Making ammonia and sulfuric acid
Cambridge IGCSE Chemistry 0620 · 10 marks · papermunch.org
Name ______________________________ Date ______________
State the temperature, pressure and catalyst used in the Haber process.[3]
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450 °C, 20 000 kPa (200 atmospheres), iron.
State the source of each raw material for the Haber process.[2]
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Nitrogen from the air; hydrogen from methane (natural gas).
The reaction that makes ammonia is exothermic. Explain why a temperature of 450 °C is used rather than a lower one.[3]
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A lower temperature would give a higher yield, but the reaction would be too slow. 450 °C is a compromise between yield and rate.
Name the catalyst used in the Contact process, and the product of the reversible reaction.[2]
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Vanadium(V) oxide; sulfur trioxide.
Answers: Making ammonia and sulfuric acid
- 1. 450 °C, 20 000 kPa (200 atmospheres), iron.
- 2. Nitrogen from the air; hydrogen from methane (natural gas).
- 3. A lower temperature would give a higher yield, but the reaction would be too slow. 450 °C is a compromise between yield and rate.
- 4. Vanadium(V) oxide; sulfur trioxide.