In any chemical reaction, the total mass of the substance before and after the reaction is the same although its matter undergoes a physical change. <br />law of definite proportions : <br />"In a chemical substance the elements are always present in definite proportions by mass". <br />Law of Multiple Proportions <br />When two elements combine to form different compounds, then the weight of one is constant and the other has a simple ratio. Read more at http://learnnext.com/lesson/CBSE-IX-Science-Atoms-and-Molecules.htm
