When calcium oxide (CaO), also known as quicklime, is added to water (H2O), it undergoes a chemical reaction to form calcium hydroxide (Ca(OH)2), commonly known as slaked lime. This reaction is exothermic, meaning it releases heat. The chemical equation for this reaction is:

CaO(s) + H2O(l) → Ca(OH)2(aq)

In this reaction, calcium oxide, a basic oxide, reacts with water, which is amphoteric, to produce calcium hydroxide, a strong base. The product, calcium hydroxide, dissolves in water to form a milky white suspension known as limewater.