When a chemical reaction takes place, one or more of the following can be observed:
a. change in colour
b. evolution of gas
c. evolution of heat
d. formation of precipitate
When ferrous sulphate crystal is heated;
a. colour changes from light green to white and then to brown.
b. gas is emitted which smells like burning sulphur.
2FeSO₄.7H₂O(s)-------------->2FeSO₄(s) -----------> Fe₂O₃(s) + SO₂(g) + SO₃(g)
(light green) (white) (brown)