Why does the solubility of a gas in a liquid generally decrease with increasing temperature?

The dissolution of a gas in a liquid is typically an exothermic process, meaning it releases heat into the surroundings. According to Le Chatelier's Principle, if an equilibrium system is subjected to a change in temperature, it will shift in a direction that counteracts that change. Therefore, increasing the temperature adds heat to the system, causing the equilibrium to shift towards the endothermic direction, which is the desorption (gas escaping from liquid) process. This results in a net decrease in the amount of gas dissolved in the liquid, hence lower solubility.

What is Henry's Law, and what are its main applications?

Henry's Law states that at a constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the surface of the liquid. Mathematically, it's often expressed as $P = K_H cdot x$, where $P$ is partial pressure, $x$ is mole fraction of the gas in solution, and $K_H$ is Henry's constant. Key applications include the carbonation of soft drinks (dissolving $ ext{CO}_2$ under high pressure), understanding decompression sickness in divers (nitrogen bubbles forming due to rapid pressure drop), and explaining anoxia at high altitudes (lower oxygen partial pressure leading to reduced oxygen solubility in blood).

Does Henry's Law apply to all gases and solvents under all conditions?

No, Henry's Law has certain limitations. It is most accurate for gases that do not chemically react with the solvent (e.g., $ ext{NH}_3$ in water) and do not dissociate or associate in the solvent. It also holds best for dilute solutions and at moderate pressures and temperatures. For instance, if a gas reacts significantly with the solvent, its 'solubility' will be much higher than predicted by Henry's Law for physical dissolution alone.

How does the nature of the gas and the solvent affect solubility?

The 'like dissolves like' principle is a good guide. Polar gases (like $ ext{HCl}$, $ ext{NH}_3$) tend to be more soluble in polar solvents (like water) due to strong dipole-dipole interactions or hydrogen bonding. Non-polar gases ($ ext{O}_2$, $ ext{N}_2$) are less soluble in polar solvents. Additionally, larger gas molecules generally exhibit higher solubility due to stronger London dispersion forces. Gases that chemically react with the solvent, such as $ ext{NH}_3$ with water, show exceptionally high solubility.

Why do deep-sea divers need to be careful about ascending too quickly?

At greater depths, the pressure increases significantly, leading to a higher partial pressure of the gases (primarily nitrogen and oxygen) in the compressed air divers breathe. According to Henry's Law, this increased pressure causes more nitrogen to dissolve in the diver's blood and body tissues. If the diver ascends too quickly, the external pressure drops rapidly, and the dissolved nitrogen becomes less soluble. This excess nitrogen forms bubbles in the blood and tissues, leading to a painful and dangerous condition called decompression sickness or 'the bends', which can cause joint pain, paralysis, or even death.

Solubility of Gas in Liquids

Chemistry

NEET UG

Version 1Updated 22 Mar 2026

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The solubility of a gas in a liquid refers to the maximum amount of that gas that can dissolve in a given quantity of the liquid at a specific temperature and pressure, forming a homogeneous solution. This phenomenon is governed by several factors, most notably the partial pressure of the gas above the liquid, the temperature of the system, and the intrinsic nature of both the gas and the solvent.…

Quick Summary

The solubility of a gas in a liquid quantifies how much gas can dissolve in a given liquid volume at specific conditions. This process involves a dynamic equilibrium between gas molecules entering and leaving the liquid phase.

The primary factors influencing this solubility are pressure, temperature, and the nature of the gas and solvent. Henry's Law states that at constant temperature, the solubility of a gas is directly proportional to its partial pressure above the liquid ( $P = K_H x$ ).

A higher Henry's constant ( $K_H$ ) implies lower solubility. Generally, gas solubility decreases as temperature increases, as dissolution is often an exothermic process. The 'like dissolves like' rule applies, meaning polar gases dissolve better in polar solvents, and non-polar gases in non-polar solvents.

Applications range from carbonated drinks to understanding physiological effects in deep-sea diving and high-altitude living, where pressure changes significantly impact gas solubility in blood.

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Key Concepts

Henry's Law and its Inverse Relationship with

K_H

Henry's Law, $P = K_H x$ , establishes a direct proportionality between the partial pressure of a gas ( $P$ )…

Effect of Temperature on Gas Solubility

Unlike most solids, the solubility of gases in liquids almost universally decreases as temperature increases.…

Nature of Gas and Solvent (Like Dissolves Like)

The specific chemical properties of both the gas and the solvent play a crucial role in determining…

Henry's Law: —

P = K_H x

(Partial pressure

propto

Mole fraction in solution)

$K_H$: — Henry's Law constant; higher

K_H

means lower solubility.

Temperature Effect: — Gas solubility generally decreases with increasing temperature (exothermic process).

Pressure Effect: — Gas solubility increases with increasing partial pressure of the gas.

Nature of Gas/Solvent: — 'Like dissolves like'; reactive gases (e.g.,

ext{NH}_3

ext{H}_2\text{O}

) show high solubility.

Units: — Ensure consistency (e.g., atm, bar, Pa) for

P

and

K_H

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Pressure: Increases solubility

Temperature: Decreases solubility

Nature: 'Like dissolves like' (polarity, reactivity)

Henry's Law:

P = K_H x

KH: Higher

K_H

means lower solubility