Here's why:

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

* Atoms are rearranged, not destroyed: In a chemical reaction, atoms are simply rearranged to form new molecules. The total number of each type of atom remains the same.

So, if you start with five hydrogen atoms, you must end up with five hydrogen atoms, even if they're part of different molecules in the products.