Law of conservation of mass
Total mass of reactants before reaction is equal to total mass of products after the reaction.
In the late 1700's, a French noble man named Antoine Lavoisier observed that the total mass of all substances present after a chemical reaction is same as total mass before the reaction. This observation, known as the law of conservation of mass, is one of the fundamental laws of chemical change. In 1789, Lavoisier published a text book on chemistry in which he stated “We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal quantity of matter exists both before and after the experiment”.
With the outcome of atomic theory chemists came to understand the basis for this law: Atoms are neither created nor destroyed during any chemical reaction. Thus number of atoms remains constant before and after the completion of reaction. The changes that occur during any reaction merely involve rearrangement of atoms. Lavoisier medal is given to honor people throughout the history of DuPont whose extraordinary technical achievements have resulted in significant business impact and enduring scientific value. With this knowledge, we now move forward to examine the quantitative nature of chemical formulas and chemical reactions. This area of study is called stoichiometry.