Question

Which of the following reactions are exothermic in nature?

(i) Evaporation of water
(ii) Dissolution of sodium hydroxide in water
(iii) Dilution of sulphuric acid
(iv) Dissolution of ammonium chloride in water
(v) Combustion of methane gas

• A. (i), (iv) and (v) only
• B. (ii), (iii) and (v) only
• C. (i), (ii) and (iv) only
• D. (i), (iii) and (iv) only

Answer 1

The correct option is B

(ii), (iii) and (v) only

Dissolution of sodium hydroxide in water, dilution of sulphuric acid and combustion of methane gas are exothermic reactions in which a large amount of heat is released.

Dissolving sodium hydroxide in water is exothermic. This is because the sodium ions and hydroxyl ions are capable of interacting with the water molecules and these interactions release energy in the form of heat. In the case of dilution of sulphuric acid, it reacts with water to form new bonds(hydrogen bonds) which liberate a large amount of energy.

Evaporation of water and dissolution of ammonium chloride in water are endothermic reactions in which heat is absorbed.