Q. Which of the following are exothermic processes ?
i. Evaporation of water.
ii. Dilution of an acid (H2SO4).
iii. Reaction of water with quick lime.
iv. Sublimation of camphor (crystals).
a) iii and iv
b) ii and iii
c) i and iv
d) i and ii
Question from BPSC PT 70, 2024
Correct Answer: b) ii and iii
Explanation:
Exothermic process
An exothermic process is one in which energy (usually in the form of heat) is released into the surroundings.
1. Evaporation of water: This is an endothermic process because water molecules absorb heat from the surroundings to overcome intermolecular forces and change from liquid to vapor. Hence, this is not exothermic.
2. Dilution of an acid (H₂SO₄): When concentrated sulfuric acid is diluted with water, a large amount of heat is released due to the highly exothermic nature of the hydration process. Hence, this is an exothermic process.
3. Reaction of water with quick lime (CaO): When water reacts with quick lime (calcium oxide), it forms slaked lime (calcium hydroxide) and releases a significant amount of heat. This is a highly exothermic reaction.
CaO + H₂O → Ca(OH)₂ + heat
4. Sublimation of camphor (crystals): Sublimation is an endothermic process because energy is absorbed to convert a solid directly into a gas without passing through the liquid phase. Hence, this is not exothermic.
Thus, the correct answer is b) ii and iii, as both the dilution of sulfuric acid and the reaction of water with quick lime are exothermic processes.
