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 2H2 十 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)