Water and calcium oxide react quickly to form slaked lime, which releases a significant amount of _________.

Slaked lime is created when calcium oxide combines vigorously with water, producing a significant quantity of heat.

Calcium hydroxide is formed when calcium oxide (commonly known as quick lime) mixes with water (commonly known as slaked lime).

$\mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\to \mathrm{Ca}\left(\mathrm{OH}{)}_2\right(\mathrm{s})$

When lime is treated with water, lots of energy is evolved, therefore it is an exothermic reaction.

Therefore, the above reaction is classified as both a combination and an exothermic reaction.