An equation is the symbolic representation of a chemical reaction based on the conservation of mass.
The law of conservation of mass states that mass can neither be created nor it can be destroyed. The volume and the density of the matter may be changing but mass will remain constant. Or it could be represented by a balanced chemical equation, which is a chemical equation that shows all mass is conserved during the entirety of the reaction. For example, N_{2} + H_{2} -----> NH _{3} is an unbalanced chemical equation. In order to balance the said equation, we need to add coefficients to equalize the number of atoms on both the reactants and product sides. This will give us a new equation and that is N_{2} + 3H_{2} -----> 2NH _{3}. Through this the mass of the atoms are conserved.