Question

Classify the following as a physical or chemical change. State a reason for the choice.

Rusting of iron.

Answer 1

Chemical change:

• A chemical change is a permanent change in which new substances are formed.
• The chemical change is permanent and cannot be reversed by a simple physical method.
• A chemical change involves an exchange of energy in the form of heat or light.
• For example, rusting of iron, burning of wood, respiration, etc.

Rusting:

• During the rusting, when a piece of iron is left out in moist air, it slowly changes into a dull brittle brown substance called rust (${\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{xH}}_2\mathrm{O}$).
• The formation of rust on the surface of iron is called the rusting of iron.
• The composition and properties of rust are different from those of iron.
• Rust cannot be converted back to iron by simple physical methods.
• This process is irreversible and permanent.

Therefore, rusting of iron is a chemical change.