Here's why:
* Physical changes only alter the appearance or form of a substance, not its chemical composition.
* The molecules of the substance remain the same, they just rearrange or change their state of matter.
Examples of physical changes:
* Melting ice: Water (H₂O) changes from solid to liquid, but the chemical composition (H₂O) remains the same.
* Boiling water: Water changes from liquid to gas (steam), but the chemical composition remains the same.
* Cutting paper: The paper is divided into smaller pieces, but the chemical composition remains the same.
In contrast, chemical changes result in the formation of new substances with different chemical compositions.
Examples of chemical changes:
* Burning wood: Wood reacts with oxygen, producing ash, carbon dioxide, and water. The original wood is gone, and new substances are formed.
* Rusting iron: Iron reacts with oxygen and water to form iron oxide (rust), a new substance with different properties.
* Baking a cake: The ingredients undergo chemical reactions, creating a new substance with a different taste, texture, and appearance than the original ingredients.
