Question

Give an example in the given case:
(a) Change which occurs on heating but can be reversed.
(b) Change that occurs on heating but cannot be reversed.
(c) Change occurs on cooling but can be reversed.
(d) Change occurs on mixing two substances but can be reversed.
(e) Change which occurs on mixing two substances, but cannot be reversed.

Answer 1

(a)

Heating of an iron rod: Only the shape of the iron changes on heating

The original shape can be obtained back again through heating and cooling.
Therefore, the above process is a reversible change.

(b)

Baking of chapati:

• Once the chapati is baked it cannot be reversed because the dough gets cooked

(c)

Conversion of ice into water and water into ice:

• Water can be converted into ice through freezing.
• Ice can be converted back into water through melting

So, the above process reversible.

(d)

Mixing sand in water:

• Sand is not soluble in water.
• Sand settles down on after mixing with water.

Hence, the process is reversible.

(e)

Mixing of cement with water:

• Hardening of cement occurs
• It is irreversible because once hardened, the original state cannot be obtained.