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SECTION B

5.The manufacture of sulphuric acid is carried out on a large scale in most industrialised countries because it is needed by many other industries. In most countries the raw material is sulphur. The process consists of three main stages - the burning of sulphur in air, the conversion of sulphur dioxide to sulphur trioxide and the formation of sulphuric acid. The equation for the conversion to sulphur trioxide is

2SO2(g)  +  O2(g)  2SO3(g)

(a)For the conversion to sulphur trioxide, the effect of temperature on the percentage yield at equilibrium is shown in Figure 1.

Figure 1

(i)State whether this reaction is exothermic or endothermic and justify your answer by reference to Figure 1.

(2)

(ii)Give the name of the catalyst used in this reaction. State the effect of the catalyst on the percentage yield at equilibrium of sulphur trioxide and on the rates of both forward and reverse reactions.

(4)

(iii)A typical operating temperature is 450 °C. State one advantage and one disadvantage of operating the process at a temperature 50 °C lower.

(2)

(b)The operating pressure for the conversion of sulphur dioxide to sulphur trioxide is slightly higher than atmospheric pressure.

(i)State the effect on the rate of the reaction of using a much higher pressure.

(1)

(ii)State the effect of using this much higher pressure on the percentage yield at equilibrium of sulphur trioxide and give a reason for your answer.

(2)

(Total 11 marks)

7

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