Question

Heat is liberated in the reactions where water is added to calcium oxide and hydrochloric acid added to zinc pieces. 

Rarnu says that they are same type of chemical reactions. Eswar’s opinion is that the reactions are not similar. What is the basis of Eswar’s opinion ? Write equations for the above reaction.

Answer 1

Eswar’s thinking is correct. Although both are exothermic reactions, the type of chemical reactions is different. 

Case (i) : When water is added to calcium oxide it forms calcium hydroxide. It is an example for combination reaction.

CaO_(s) + H₂O → Ca(OH)_2(aq)

Case (ii) : When hydrochloric acid is added to zinc pieces it would liberate hydrogen gas which is an example for displacement reaction.

Zn_(s) + HCl_(aq) → ZnCl_2(aq) + H_2(g) ↑