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CAIE IGCSE Chemistry Catalysts and Reaction Rate

Practise defining a catalyst as a substance that increases reaction rate while remaining chemically unchanged and distinguishing rate from final yield.

Syllabus
2026–2028
Course
Chemistry 0620

Exam points

  • define a catalyst as increasing reaction rate while remaining chemically unchanged at the end
  • state that a catalyst changes how quickly products form but not the final stoichiometric amount
  • recognise that a catalyst can permit a lower operating temperature or pressure for a useful rate

6.2.2—Catalyst increases the rate of a question 1

[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, H2 S2O7\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.

2SO2+O2⇌2SO32 \mathrm{SO}_{2}+\mathrm{O}_{2} \rightleftharpoons 2 \mathrm{SO}_{3}

The reaction is carried out at a temperature of 450∘C450^{\circ} \mathrm{C} and a pressure of 1-2 atmospheres using a catalyst. The energy change, ΔH\Delta H, for the reaction is −196 kJ/mol-196 \mathrm{~kJ} / \mathrm{mol}.

Why is a catalyst used?

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