The reaction between CaO (calcium oxide) and HCl (hydrochloric acid) results in the formation of calcium chloride (CaCl2) and water (H2O). The chemical equation for this reaction is:

CaO + 2HCl → CaCl2 + H2O

In this reaction, calcium oxide acts as a base, while hydrochloric acid acts as an acid. The reaction is a classic example of an acid-base neutralization reaction.