Definition & Concept of the Law

The Law of Conservation of Mass states that in any chemical reaction occurring in a closed system, the total mass of the reactants (the starting substances) is equal to the total mass of the products (the substances formed).

In simpler terms: mass is neither created nor destroyed during a chemical reaction. It just changes form.

This means that the amount of "stuff" (matter) you start with is the same amount you end with, even if it looks very different.