When calcium oxide (CaO), also known as quicklime, is added to hydrochloric acid (HCl), it undergoes a chemical reaction to form calcium chloride (CaCl2) and water (H2O). The overall reaction can be represented as follows:

CaO(s) + 2HCl(aq) → CaCl2(aq) + H2O(l)

In this reaction, calcium oxide reacts with the hydrogen ions (H+) from the hydrochloric acid to form water molecules, while the calcium ions (Ca2+) combine with the chloride ions (Cl-) to produce calcium chloride. The product, calcium chloride, is a water-soluble salt that can be dissolved in the solution.

The reaction between calcium oxide and hydrochloric acid is exothermic, which means that it releases heat. As a result, the solution formed during the reaction may become hot and emit steam due to the evaporation of water. It is important to handle the reaction with caution and wear appropriate safety gear, including gloves and eye protection.