Combination of water and calcium oxide (cao) generates heat which causes some of water to evaporate and subsequently, lime is swollen due to water absorption. Then the lime turns into a white powder which is called hydrated lime.
This solid odorless (solid odorless) material with hexagonal crystals or soft white granules disintegrates (dissolves) in 580 c before reaching to boiling point. It is soluble in acids and ammonium salt solutions and insoluble in ethanol; it quickly absorbs air co2 (co2 from the air) and turns into calcium carbonate. When (some) water is added to hydrated lime, it turns into lime water which if it is filtered (and if filtered), a clear solution called calcium hydroxide, is obtained. It has many applications in chemical industries, such as preparation of sodium hydroxide, ammonium, per chlorine and it is specifically used to extract magnesium from seawater.