An example of a reversible chemical change is thermal decomposition of salts such as hydrates copper-sulphate results in the dehydration of the salt.
CuSO 4 .5H 2 O ———–> CuSO 4 (s) + 5H 2 O (g)
In this reaction, colour changes from blue to white. Water is removed from the copper sulphate. This dehydration reaction can be reversed by slowly adding water back to the powder. This reaction is exothermic and the blue colour of the powder is retained.
CuSO 4 (s) + 5H 2 O ————> CuSO 4 .5H 2