CAIE IGCSE Chemistry 6.3.1 Some chemical reactions are reversible

Practise recognising reversible reactions from the ⇌ symbol and from changes that can be undone by reversing conditions.

Exam points

state that the ⇌ symbol shows a reversible reaction or equilibrium

[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 $-196 \mathrm{~kJ} / \mathrm{mol}$ .

What is the meaning of the symbol ⇌?

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6.3.1—Some chemical reactions are reversible question 1