Henry’s Law and Gas Solubility in Liquids

Henry’s Law and Gas Solubility in Liquids

Introduction to Henry’s Law

Henry’s Law describes the relationship between the solubility of a gas in a liquid and the partial pressure of that gas above the liquid. This principle is essential for understanding how gases dissolve in solutions, which is a key concept in chemistry.

• Henry’s Law Statement: The solubility of a dissolved gas is directly proportional to the partial pressure of that gas over the liquid.

Pressure–Solubility Relationship

Increasing the pressure of a gas above a liquid increases the solubility of the gas in the liquid. This is because more gas molecules are 'forced' into the solution at higher pressures.

• Key Point: As the pressure increases, the solubility of a gas in a liquid increases.

• Equation:

$C = k_P P$

• Where $C$ is the concentration (solubility) of the gas, $k_P$ is Henry’s law constant, and $P$ is the partial pressure of the gas.

Temperature–Solubility Relationship

The solubility of gases in liquids generally decreases as temperature increases. Higher temperatures give gas molecules more kinetic energy, making them more likely to escape from the liquid phase into the gas phase.

• Key Point: As the temperature increases, the solubility of a gas in a liquid decreases.

Example

In general, as the temperature increases, the solubility of a gas in a given liquid decreases, and the solubility of most solids in a given liquid increases.

• Correct Answer: (c) Decreases, increases

Practice Question

Which of the following is true for the solubility of NaCl (s) and CH4 (g) in water?

• Increasing the temperature will increase the solubility of NaCl.

• Increasing the temperature will decrease the solubility of CH4.

• Correct Answer: (b) Both NaCl (s) and CH4 (g) are soluble in water.

Additional info: The solubility of most solids increases with temperature, while the solubility of gases decreases with temperature. Henry’s Law is particularly important for understanding phenomena such as the behavior of carbonated beverages and the oxygenation of water in aquatic environments.