Here's why:

* Chemical Changes Break and Form Bonds: Chemical changes involve the breaking and forming of chemical bonds between atoms. This rearrangement of atoms leads to entirely different molecules with different properties.

* New Properties, New Substances: The new molecules formed during a chemical change have different chemical and physical properties than the original substances. For example, burning wood (a chemical change) produces ashes, carbon dioxide, and water - all substances different from the original wood.

Examples of Chemical Changes:

* Burning wood

* Rusting iron

* Baking a cake

* Cooking an egg

Remember: If there's no change in the chemical composition of the substance, it's a physical change.