The Contact Process — Industrial Conditions
15 Questions · 36 Marks · Temperature, Pressure & Catalyst Analysis
Process Overview
Section A — Stating Conditions
5 Questions
State the three conditions used in the Contact process for the conversion of SO₂ to SO₃.
Write the equation for the key reaction in the Contact process. Include a sign for the reversible reaction and state symbols.
Name the catalyst used in the Contact process and explain what type of catalysis this is.
The Contact process operates at 450°C. State whether this is a high or moderate temperature compared to many industrial processes, and identify what the catalyst does at this temperature.
After SO₃ is formed in the Contact process, it is NOT dissolved directly in water. State what it is dissolved in instead, and give the name of the product formed.
Section B — Temperature Analysis
5 Questions
The forward reaction in the Contact process is exothermic. Explain why a very high temperature of 800°C is NOT used, even though it would increase the rate of reaction.
Explain why a very low temperature of 100°C is also NOT used in the Contact process, even though it would give a higher yield of SO₃.
The Contact process uses a temperature of 450°C. Using Le Chatelier's principle, explain what happens to the equilibrium position if the temperature is increased above 450°C.
The 450°C temperature in the Contact process is described as a 'compromise temperature.' What are the two competing factors that make this a compromise?
Define Le Chatelier's principle and apply it to explain how a decrease in temperature would affect the equilibrium position in the Contact process.
Section C — The Pressure Trap
5 Questions
⚡ Mole Counter — Why Pressure Shifts Right
LEFT SIDE
2SO₂(g) + O₂(g)
3 mol gas
RIGHT SIDE
2SO₃(g)
2 mol gas
↑ Pressure → Equilibrium shifts to side with FEWER gas moles → shifts RIGHT ✓
The equation for the Contact process is: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g). Using Le Chatelier's principle, explain why increasing pressure shifts the equilibrium to the RIGHT.
High pressure increases the yield of SO₃. Explain why a low pressure of only 2 atm (200 kPa) is used in the Contact process instead of a very high pressure.
A student claims: 'The Contact process should use 200 atm pressure to maximise the yield of SO₃.' Evaluate this claim. Is the student correct? Give TWO reasons for your answer.
Compare the pressure used in the Contact process (2 atm) with the pressure used in the Haber process (200 atm). Suggest why the Contact process can operate profitably at such a low pressure.
Suggest what would happen to the economic viability of the Contact process if the price of vanadium(V) oxide catalyst doubled. Give a reason for your answer.
Exam Summary
Total: 36 marks
Section A
11 marks
Section B
12 marks
Section C
13 marks
🎯 Paper 4 Golden Rule
Always explain the ECONOMIC reason for low pressure (98–99% yield already achieved) — not just the chemical reason. This earns the third mark every time.
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