State symbols in chemical equations

A chemical equation can show the physical state of each reactant and product as well as its formula. A state symbol is written in brackets immediately after the formula of the substance it describes.

(s) means solid.
(l) means liquid.
(g) means gas.
(aq) means aqueous: the substance is dissolved in water to form a solution.

The distinction between (l) and (aq) matters. For example, $\ce{H2O(l)}$ represents liquid water, whereas $\ce{NaCl(aq)}$ represents sodium chloride dissolved in water, not liquid sodium chloride.

Choosing state symbols

Choose the symbol for each reactant and product from its actual state under the reaction conditions given. A salt dissolved in water is aqueous, while an insoluble solid formed in a reaction is written as a solid.

For example, when aqueous silver nitrate reacts with aqueous sodium chloride, solid silver chloride forms:

\ce{AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq)}

The symbols show that silver nitrate, sodium chloride and sodium nitrate are dissolved in water, while silver chloride is a solid. Including the correct state symbol for each substance makes the equation more precise and is part of writing a complete chemical equation.