Question

What do you understand by physical change
and chemical change? Classify the following as
physical or chemical changes :
(i) Dissolving salt in water
(ii) Electric current is passed through water and
it is broken down into hydrogen and oxygen
(iii) Evaporation of alcohol
(iv) Digestion of food

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Answer 1

Physical changes only lead to changes in physical properties of the substance and are reversible chemical changes lead to change in composition or the structure and are irreversible in nature.

(a) Photosynthesis: irreversible, chemical changes.

6CO

2

+6H

2

O⟶C

6

H

12

O

6

+6O

2

(b) Dissolving of water : reversible, physical change.

(c) Bumping of coal − irreversible, chemical change.

(d) Melting of wax − reversible by cooling, physical change.

(e) Physical change as mallacbility (beating metal into then sheets) does not change composition.

(f) Digestion − chemical change.