Law of mass conservation(质量守恒定律 matter is neither created nor destroyed during a chemical reaction. The finding of oxygen resulted from this law The chemical equation must be balanced(平衡) Two hydrogen molecules One oxygen molecule Two water molecules 2H 2H,OLaw of mass conservation (质量守 恒定律 ): matter is neither created nor destroyed during a chemical reaction. The finding of oxygen resulted from this law. The chemical equation must be balanced (平衡)