On heating the ferrous sulphate crystals loses water and becomes anhydrous ferrous sulphate. It also changes its colour from green to white.

FeSO₄.7H₂O→FeSO₄ + 7H₂O

If we further heat ferrous sulphate then decomposition occurs and ferric oxide, sulphur dioxide and sulphur trioxide are formed as a result of decomposition.

FeSO₄→Fe₂O₃ + SO₂ + SO₃