The solubility of a gas in a liquid decreases with rise in temperature. Which of the following is the reason for this?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Dissolution of a gas in a liquid is an exothermic process.
When a gas dissolves, its molecules pass into the liquid phase, much like condensation, and heat is given out. Dissolution is a dynamic equilibrium, so by Le Chatelier’s principle raising the temperature shifts it back, and less gas stays dissolved.
Why the other options are incorrect
Option (2) Dissolution of a gas in a liquid is an endothermic process. — Incorrect. If dissolution were endothermic, heating would increase the solubility, as it does for a solid with ΔsolH > 0.
Option (3) The Henry’s law constant (KH) of a gas decreases with rise in temperature. — Incorrect. KH increases with temperature (Table 1.2 values for N2 and O2), and a higher KH means a lower solubility.
Option (4) Dissolution of a gas in a liquid does not involve a dynamic equilibrium. — Incorrect. The dissolution of a gas does involve a dynamic equilibrium, which is why Le Chatelier’s principle applies to it.
NCERT (2026-27 edition):
1.3.2 Solubility of a Gas in a Liquid – “Solubility of gases in liquids decreases with rise in temperature. When dissolved, the gas molecules are present in liquid phase and the process of dissolution can be considered similar to condensation and heat is evolved in this process. We have learnt in the last Section that dissolution process involves dynamic equilibrium and thus must follow Le Chatelier’s Principle. As dissolution is an exothermic process, the solubility should decrease with increase of temperature.”