Question

(a) Discuss some characteristics of chemical changes.
(b) Classify the following processes into physical or chemical changes:

(i) Beating of aluminium metal to make aluminium foil.
(ii) Digestion of food.
(iii) Cutting of a log of wood into pieces.
(iv) Rusting of iron.

Answer 1

(a) The characteristics of chemical changes are:

1) It is a permanent and irreversible change.
2) New substances are formed in this change.
3) Energy in the form of heat or light is either absorbed or released.

(b)
(i) In the given examples, beating of aluminium metal to make aluminium foil and cutting of a log of wood into pieces are physical changes as there is no change in their composition.
(ii) Digestion of food is a chemical change as the food breaks down and forms new substance inside the stomach.
(iii) Rusting of iron is a chemical change as a reddish-brown flaky layer (rust) is formed on its surface when it is left in air.