what is the law of conservation of mass

The law of conservation of mass states that, in a closed or isolated system, matter cannot be created or destroyed. It can change forms but is conserved. This law is a fundamental principle in physics and chemistry, and it was first discovered by Antoine Lavoisier in 1789. During a chemical reaction, the total mass of the products must be equal to the total mass of the reactants, which means that mass is neither created nor destroyed in a chemical reaction