In the equation H2 + N2 → NH3, the reactants are both H2 and N2. In this equation, the two reactants of hydrogen and nitrogen react to form ammonia gas. In a chemical equation, the components on the left side are the reactants and those on the right are products.
Another example of a reactant is found in the equation 2 H2O → 2 H2 + O2 where water produces both oxygen and hydrogen gas. In this reaction, the reactant is H2O, the water, and the products are the gases H2 and O2. This type of reaction is called decomposition.
In an acid-base reaction, such as HBr + NaOH → NaBr + H2O, HBr, hydrobromic acid and NaOH, the base sodium hydroxide, are reactants that interact to form the products of sodium bromide and water. In this acid-base reaction, the H+ from the hydrobromic acid reacts with OH- from the base.
In a combustion reaction, such as the burning of naphthalene, the reactants are C10H8 and O2, which react to form carbon dioxide and water. This reaction is illustrated with the equation C10H8 + 12 O2 → 10 CO2 + 4 H2O with the reactants on the left side and the products on the right.