Phosphorus pentachloride hydrolysis. Spatula of phosphorus pentachloride (PCl5) being added to a petri dish of water (H2O). A reaction with water is called a hydrolysis reaction. The products of the reaction are phosphoric acid (H3PO4) and hydrochloric acid (HCl). The reaction equation is: PCl5 + 4.H2O -----> H3PO4 + 5.HCl