CAIE IGCSE Chemistry 6.3.11 Typical Haber & Contact process

Practise explaining why industrial Haber and Contact process conditions balance reaction rate, equilibrium yield, safety and cost.

Exam points

explain how changing temperature or pressure affects rate and equilibrium yield
link catalysts to faster forward and reverse reactions without changing equilibrium yield
justify why lower temperatures or higher pressures may be impractical or expensive

[Maximum number: 1]

Sulfuric acid can be manufactured from the raw materials sulfur, air and water. The process can be divided into four stages.
stage 1 converting sulfur into sulfur dioxide
stage 2 converting sulfur dioxide into sulfur trioxide
stage 3 converting sulfur trioxide into oleum, $\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}$
stage 4 converting oleum into sulfuric acid
stage 1

Sulfur dioxide is converted into sulfur trioxide according to the following equation.

2 \mathrm{SO}_{2}+\mathrm{O}_{2} \rightleftharpoons 2 \mathrm{SO}_{3}

The reaction is carried out at a temperature of $450^{\circ} \mathrm{C}$ and a pressure of 1-2 atmospheres using a catalyst. The energy change, $\Delta H$ , for the reaction is $-196 \mathrm{~kJ} / \mathrm{mol}$ .

Suggest a reason why a temperature lower than $450^{\circ} \mathrm{C}$ is not used.

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6.3.11—Typical Haber and Contact process question 1