When ferrous sulphate is heated, it undergoes a process called thermal decomposition. This process involves the breakdown of the compound into its constituent elements or simpler compounds due to the application of heat.

The balanced chemical equation for the thermal decomposition of ferrous sulphate is:

2FeSO4(s) → Fe2O3(s) + SO2(g) + SO3(g)

In this reaction, ferrous sulphate (FeSO4) decomposes to form iron(III) oxide (Fe2O3), sulphur dioxide (SO2), and sulphur trioxide (SO3). Iron(III) oxide is a reddish-brown solid, sulphur dioxide is a colourless gas with a pungent odour, and sulphur trioxide is a colourless gas with a choking odour.

The thermal decomposition of ferrous sulphate is a chemical change because the starting material (ferrous sulphate) is converted into different products (iron(III) oxide, sulphur dioxide, and sulphur trioxide). This change is irreversible, meaning that the original compound cannot be recovered from the products.