The total amount of matter before and after a chemical reaction remains the same.
Mass is the amount of matter in something. As per the first postulate of Daltons atomic theory, all matter is made up of atoms. The third postulate of the same theory asserts that atoms can be neither created nor destroyed in a chemical reaction, i.e., the total number of atoms and their mass should remain the same before and after the reaction. This is the same as the law of conservation of mass.how