Question

Rusting of iron is a _________ change while freezing of water is a ____________change.

• A. chemical
• B. physical

Answer 1

Chemical change:

• During a chemical change, the substances undergo a chemical reaction.
• As a result of this, new substances (products) are formed which differ in their chemical composition from the original substances.
• For example, When an object made of iron$\left(\mathrm{Fe}\right)$ comes in contact with moist air for some time, it undergoes a chemical change and forms iron oxide, a reddish-brown powdery substance called rust($\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$
• $\underset{\mathrm{iron}}{4\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{oxygen}\mathrm{from}\mathrm{moist}\mathrm{air}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}\stackrel{}{\to }\underset{\mathrm{rust}}{2{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}$

Physical change:

• When a substance may undergo a change in some of its physical properties like colour, size, or shape, but does not undergo any change in its chemical composition is known as physical change.
• For example freezing of water is a physical change.

Therefore, Rusting of iron is a chemical change while freezing of water is a physical change.