Question

Translate the following statement into a chemical equation and then balance it:

Hydrogen sulphide gas burns in the air to give water and sulphur dioxide. [3 Marks]

Answer 1

The chemical equation for the given chemical reaction is:
${\text{H}}_2\text{S(g)}+{\text{O}}_2\text{(g)}\to {\text{H}}_2\text{O(l)}+{\text{SO}}_2\text{(g)}$
[1 Mark]

The number of oxygen atoms on the reactant and product side is not balanced. So we need to add a coefficient 3 before ${\text{O}}_2$ in the reactant side and 2 before ${\text{H}}_2\text{O}$ and ${\text{SO}}_2$ in the product side.
Therefore the equation becomes:
${\text{H}}_2\text{S(g)}+3{\text{O}}_2\text{(g)}\to 2{\text{H}}_2\text{O(l)}+2{\text{SO}}_2\text{(g)}$
[1 Mark]

In order to balance the number of sulphur atoms, add a coefficient 2 before ${\text{H}}_2\text{S}$ in the reactant side.

The balanced chemical equation is:
$2{\text{H}}_2\text{S(g)}+3{\text{O}}_2\text{(g)}\to 2{\text{H}}_2\text{O(l)}+2{\text{SO}}_2\text{(g)}$
[1 Mark]