Question

Give reason:

(a)Freezing of water to ice and evaporation of water are physical changes.

(b)Burning of a candle is both a physical and a chemical change.

(c)Burning of paper is a chemical change.

(d)Cutting of a cloth piece is a physical change, though it cannot be reversed.

Answer 1

(a) Freezing of water to ice and evaporation of water are physical change because water can be
brought back to its original (liquid) form by
1. We can heat the ice to bring it back to water.
2. We can cool down the vapours to bring it back to water.
(b) When a candle is lighted, some of the solid wax rst melts and turns into liquid, then it turns into
vapours to produce a ame. New substances CO 2 and H 2 O vapours are formed alongwith the
evolution of light and heat energy. This shows a chemical change. When some of the molten waxdrops to the oor, it again solidi es. Which shows a physical change. Thus the melting of candle wax
is a physical change and the production of CO 2 and H 2 O represents chemical change.
(c) When a piece of paper is burnt a new substance ash is produced. Even when the burning is
stopped, the ash cannot be changed back into paper. This shows that the formation of the ash from
paper is a permanent and irreversible change.
(d) Because it does not change chemical composition of cloth and the change is only in the state, size,
shape, colour, texture or the smell of some or all of the substances that undergo physical change.