* Chemical Change: Involves the formation of new substances with different chemical properties. This happens through chemical reactions where bonds are broken and reformed.

* Physical Change: Alters the physical properties of a substance, such as its shape, size, or state of matter, but not its chemical composition.

When you bend a glass tube:

* The glass molecules are still the same. The chemical bonds within the glass remain intact.

* The shape of the glass changes, but the chemical composition stays the same (silicon dioxide, sodium oxide, calcium oxide, etc.).

* You can reverse the change by heating and reshaping the glass.

Examples of physical changes:

* Melting ice (water changes from solid to liquid)

* Cutting paper (changes shape but still paper)

* Dissolving sugar in water (changes state but sugar is still present)

Examples of chemical changes:

* Burning wood (forms ash, smoke, and gases)

* Rusting iron (iron reacts with oxygen to form iron oxide)

* Baking a cake (ingredients react to form a new product)