Relate the writing and balancing of a chemical equation to the principal of conservation of mass

Balancing a chemical reaction:

The reactants are written in terms of their chemical formula on the left hand side and the products are written in terms of their chemical formula on right hand side separated by an right arrow. The chemical symbols are followed by their physical states such as (l) for liquid, (s) for solid, (g) for gas and (aq) for aqueous.

The number of atoms on both sides of a  reaction must be equal in order to obey the law of conservation of mass.

Law of conservation of mass says the mass of reactants must be equal to the mass of products.

This is only possible when the reactants used are produced as products in the same quantities. Thus balancing of equation is done to follow the law of conservation of mass.