Physical states of reactants and products are mentioned while writing a chemical equation.

i.                     To make a chemical equation more informative, the physical states of the reactants and products are mentioned along with their chemical formulae.

ii.                    The gaseous, liquid, aqueous and solid states of reactants and products are represented by the notations (g), (l), (aq) and (s) respectively.

iii.                  The word aqueous (aq) is written if the reactant or product is present as a solution in water.