Quicklime (CaO)

Preparation: $CaCO_3 \xrightarrow{1073\ K} CaO + CO_2\uparrow$

Reaction with water (slaking): $CaO + H_2O \rightarrow Ca(OH)_2\ \ (\Delta H = -65\ kJ/mol,\ exothermic)$

Uses: Cement manufacturing, steel (removes silica as slag: CaO + $SiO_{2}$ → $CaSiO_{3}$ as slag), water treatment