The reaction of magnesium oxide (MgO) with hydrochloric acid (HCl) produces magnesium chloride (MgCl2) and water (H2O). The chemical equation for this reaction is:

MgO + 2HCl → MgCl2 + H2O

In this reaction, the magnesium oxide reacts with the hydrochloric acid to form magnesium chloride and water. The magnesium chloride is a salt that is soluble in water, while the water is a liquid. The reaction between magnesium oxide and hydrochloric acid is a classic example of an acid-base reaction, in which an acid (HCl) reacts with a base (MgO) to produce a salt (MgCl2) and water (H2O).