The law of conservation of mass in chemical reactions states that the same number of atoms of each element present in the reactants are present in the products.
So, the law of conservation of mass reveals that the reactants for a reaction where the products are NaCl and H2O contain the same elements and the same number of each: Na, Cl, H and O.
For example, the reaction may have been: NaOH + HCl ---> NaCl + H2O.
In a chemical reaction, the atoms are not created nor destroyed; the same atoms of each alement are present in reactants and products.
