Conservation of mass

The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. Thus, the amount of matter cannot change. Sir Antoine Lavoisier promoted this idea.

This law says that when a chemical reaction rearranges atoms into a new product, the mass of the reactants (chemicals before the chemical reaction) is the same as the mass of the products (the new chemicals made). More simply, whatever you do, you will still have the same amount of stuff.

The law is accurate for all chemical reactions. However, certain nuclear reactions (fusion and fission) can convert a small part of the mass into energy. But if this energy is turned back into mass, you will have the same amount of mass.