An Arrhenius acid is a compound that increases the concentration of H+ ions that are present when added to water. These H+ ions form the hydronium ion (H3O+) when they combine with water molecules. This process is represented in a chemical equation by adding H2O to the reactants side.
HCl(aq)→H+(aq)+Cl−(aq)
In this reaction, hydrochloric acid (HCl) dissociates into hydrogen (H+) and chlorine (Cl-) ions when dissolved in water, thereby releasing H+ ions into solution. Formation of the hydronium ion equation:
HCl(aq)+H3O+(l)→H3O+(aq)+Cl−(aq)