7th Class Science Physical and Chemical Changes Physical and Chemical changes

Physical and Chemical Changes

Synopsis

• Most of the changes occurring around us can be classified into physical and chemical changes.

• Properties like the shape, size, colour and the state of a substance are called physical properties.

• A change in the physical properties of a substance is called a physical change.

• Physical changes are usually reversible and no new substances are formed.

• A change in which one or more new substances are formed is called a chemical change.

• Chemical changes take place because of chemical reactions.

• Exchange of heat, light, sound, smell or colour can be observed in chemical changes.

• Chemical changes are irreversible.

• The process of coating iron with a layer of zinc to protect it from rusting is called galvanization.

• The formation of large crystals of pure substances from their solutions is called crystallization. It is a physical change.

• Differences between physical and chemical changes: