Question

Give two examples for each of the following cases:​

(a) Physical changes which are reversible.​
(b) Physical changes which are not reversible.
(c) Chemical changes.

Answer 1

(a) Physical changes which are reversible:​
Melting of ice- The solid form of water changes to liquid form.​
Melting of wax- The solid form of the wax melts into a liquid state during the burning of a candle.​
(b)

Physical changes which are not reversible:​

The chemical composition doesn’t change but after such processes the original condition of matter cannot be recovered.​

Example-​

• Tearing paper​

• Breaking of glass​
  

(c)

Chemical changes: ​

• Cooking of food- The raw materials used to prepare food cannot be recovered back after cooking as their chemical composition changes. ​

• Curdling of milk- The milk converts from liquid form to a semi-solid form, and the taste becomes sour, all these changes occur by change in the chemical composition of milk.​