Question

Write a balanced chemical equation which represents thermal decomposition of ferrous sulphate.

Answer 1

Decomposition reactions

Reactions in which a single reactant is broken down into more than one product are called decomposition reactions. These reactions involve the breaking of chemical bonds and are therefore endothermic. This means energy is required for the process. The energy for decomposition is absorbed by the reactants in the form of heat, light or electricity.

Decomposition reactions that occur by the absorption of heat are called thermal decomposition reactions.

Thermal decomposition of ferrous sulphate

Ferrous sulphate $\left({\mathrm{FeSO}}_4\right)$ undergoes decomposition when heated to form a solid ferric oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$, gaseous sulphur dioxide $\left({\mathrm{SO}}_2\right)$ and sulphur trioxide $\left({\mathrm{SO}}_3\right)$ gas.

The equation for the decomposition is:

${\mathrm{FeSO}}_4\left(\mathrm{s}\right)\to {\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{g}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{SO}}_3\left(\mathrm{g}\right)$

Balancing the chemical equation

The given equation has an unequal number of iron, oxygen and sulphur atoms. Two is placed as a coefficient in front of ferrous sulphate and the overall equation gets balanced. The balanced equation is given below:

$2{\mathrm{FeSO}}_4\left(\mathrm{s}\right)\to {\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{g}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{SO}}_3\left(\mathrm{g}\right)$

The green crystals of ferrous sulphate are converted into reddish-brown ferric oxide on heating due to decomposition. Thus, it is an example of a decomposition reaction.