Question

(a) Differentiate between physical and chemical changes.
(b) Give reasons:
(i) Ripening of fruit is a desirable change.
(ii) Curdling of milk is a slow change.
(ii) Digestion of food is an irreversible change.

Answer 1

(a)

PHYSICAL CHANGE	CHEMICAL CHANGE
No new Substance is formed	New substance is formed
Temporary change	Permanent change
Little changes in energy are involved	Large changes in energy are involved
e.g. Melting of ice	e.g. Burning of paper

(b) (i) Ripening of fruits is a desirable change because this change is beneficial for mankind and we desire to happen.
(ii) The process of curdling milk required hours to take place, that’s why it is considered a slow change.
(iii) Digestion of food is an irreversible change as new products are formed, and original ones cannot be re-obtained.