Here's why:

* New Substances: Chemical reactions involve the breaking and forming of chemical bonds, leading to the creation of entirely new substances with unique properties.

* Different Properties: The properties of the new substances (like color, odor, melting point, etc.) are different from the original substances that reacted.

Example:

Burning wood is a chemical reaction. Wood (made of cellulose, lignin, etc.) reacts with oxygen in the air. The reaction produces ash, carbon dioxide, water, and heat. The ash, carbon dioxide, water, and heat are entirely different substances from the original wood and oxygen, with different properties.