chemical equation

Method of indicating the reactants and products of a chemical reaction by using chemical symbols and formulae. A chemical equation gives two basic pieces of information: (1) the reactants (on the left-hand side) and products (right-hand side); and (2) the reacting proportions (stoichiometry) - that is, how many units of each reactant and product are involved. The equation must balance; that is, the total number of atoms of a particular element on the left-hand side must be the same as the number of atoms of that element on the right-hand side.

Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O

reactants → products

This equation states that one molecule of sodium carbonate combines with two molecules of hydrochloric acid to form two molecules of sodium chloride, one of carbon dioxide, and one of water. Double arrows indicate that the reaction is reversible - in the formation of ammonia from hydrogen and nitrogen, the direction of the reaction depends on the temperature and pressure of the reactants.

3H₂ + N₂ ⇌ 2NH₃