1. The substance X is the chemical compound called calcium oxide. It is called quicklime or burnt lime. The formula for calcium oxide is CaO.
Characteristics of Calcium oxide:
White or gray-white solid substance
Occurs in the form of hard lumps
Cubic hygroscopic crystals
2. The reaction of calcium oxide (substance X) with water is written as follows:
CaO (s) + H2O (l) ⇌ Ca(OH)2 (aq)
Calcium Hydroxide is called slaked lime. The reaction is accompanied by production of enormous heat (thermal energy) by formation of hydrate Ca(OH)2
The reaction is exothermic in nature.