Here's why:

* The Law of Conservation of Mass: This fundamental law of chemistry states that matter cannot be created or destroyed in ordinary chemical reactions.

* Chemical Reactions Rearrange Atoms: Chemical changes involve the breaking and forming of chemical bonds. This rearranges the way atoms are connected, but the total number of each type of atom remains the same.

Example:

Consider the burning of wood. Wood (made of carbon, hydrogen, and oxygen) reacts with oxygen in the air. The products are carbon dioxide, water, and ash. The total number of carbon, hydrogen, and oxygen atoms before and after the reaction remains constant. They are simply rearranged into new molecules.