Effect of heat on hydrate iron II sulphate pentahydrate

On heating, iron(II) sulfate first loses its water of crystallization and the original green crystals are converted into a white anhydrous solid.

FeSO₄.7H₂O(s) → FeSO₄(s) + 7H₂O(l)

When further heated, the anhydrous material decomposes into sulfur dioxide and sulfur trioxide, leaving a reddish-brown iron(III) oxide

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