Yes, the reaction of calcium oxide with water is exothermic.
When solid calcium oxide (CaO), also known as quicklime, reacts with water (H₂O), it forms calcium hydroxide (Ca(OH)₂), also known as slaked lime. This process releases a significant amount of heat. This heat liberation is what defines an exothermic reaction. The reaction is vigorous and readily observable through the increase in temperature.
The chemical equation for the reaction is:
CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
This process is called slaking of lime and is commonly used in various industrial and construction applications. The release of heat is a key characteristic of this reaction. Therefore, it's definitively exothermic.
