1. The main use of sulfur dioxide is the manufacture of sulfuric acid.

The Contact process changes sulfur dioxide into sulfur trioxide.

2SO₂ (g) + O₂ (g) $\rightleftharpoons$ 2SO₃ (g)

The forward reaction is exothermic
Temperature 400 to 450 °C
Low pressure 1 to 10 atmospheres
Catalyst vanadium(V) oxide

i) What is the formula of vanadium(V) oxide?

[1]

ii) Vanadium(V) oxide is an efficient catalyst at any temperature in the range 400 to 450 °C. Scientists are looking for an alternative catalyst which is efficient at 300°C. What would be the advantage of using a lower temperature?

[2]

iii) The process does not use a high pressure because of the extra expense. Suggest two advantages of using a high pressure? Explain your suggestions.

[4]