Here's why:
* Physical changes alter the form or appearance of a substance but don't change its chemical composition. The molecules themselves remain the same.
* Chemical changes involve the formation of new substances with different chemical compositions. The molecules are rearranged and broken apart to form new molecules.
Examples of physical changes:
* Melting ice: Water (H₂O) changes from a solid to a liquid, but the chemical makeup remains the same.
* Boiling water: Water changes from a liquid to a gas, but the chemical makeup remains the same.
* Cutting paper: The paper is broken into smaller pieces, but the chemical composition of the paper doesn't change.
Examples of chemical changes:
* Burning wood: Wood reacts with oxygen, producing ash, carbon dioxide, and water – completely different substances.
* Baking a cake: The ingredients (flour, sugar, eggs, etc.) react and change into a new substance, cake.
* Rusting iron: Iron reacts with oxygen and water to form iron oxide (rust), a different substance.
