STUDENT SPACE · TOPIC 3

Sulfur compounds and the Contact process

Explain sulfur trioxide formation and link sulfur emissions to control methods.

The essentials

Burning sulfur or roasting sulfide ores provides SO₂ for the Contact process. Oxygen comes from air.
2SO₂(g) + O₂(g) ⇌ 2SO₃(g). The forward reaction is exothermic.
Lower temperature favours SO₃ but slows the reaction. Higher pressure favours the side with fewer gas molecules.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

Would very high pressure improve SO₃ equilibrium yield? Why is it not normally used?

Need a hint for Question 1?

Write the balanced gas equation. Count gas molecules on each side.

Check Question 1

Yes, it favours fewer gas molecules. A good yield already occurs near 2 atm, so the extra cost and risk are not justified.

State the Contact catalyst, temperature and pressure.

Need a hint for Question 2?

Recall the conditions for SO₂ oxidation, not ammonia production.

Check Question 2

Vanadium(V) oxide; 450 °C; 2 atm (200 kPa).

Explain why calcium oxide can remove sulfur dioxide from waste gas.

Need a hint for Question 3?

Compare the acid–base character of CaO and SO₂.

Check Question 3

CaO is basic and reacts with acidic SO₂, reducing SO₂ emissions and acid rain.

Use Lesson 3 in your worksheet for written practice. Your teacher will discuss those answers in class.