Question

An element 'a' reacts with water to form a compound 'b' which is used in white washing . The compound 'b' on heating forms an oxide 'c' which on treatment with water gives back heat . Identify 'a' , 'b' , 'c' .How do these reactions take place ? what type of reactions are these ?

Answer 1

Element 'a': Calcium

Compound 'b': Calcium hydroxide - Ca+2H₂O--->Ca(OH)₂+H₂

Compound 'c': Calcium oxide - Ca(OH)₂--->CaO+H₂O

Adding water to CaO will produce Ca(OH)₂ which is a very strong exothermic reaction.