Here's why:

* Physical changes only alter the *form* or *appearance* of a substance, not its chemical composition.

* Chemical changes result in the formation of new substances with different chemical properties.

Here's a simple breakdown:

* Physical Change: Ice melting into water. The water molecules remain the same (H₂O), just in a different state of matter.

* Chemical Change: Burning wood. The wood reacts with oxygen, creating ash, smoke, and gases – completely different substances.

In short, physical changes are temporary and reversible, while chemical changes are permanent and create new substances.