Solutions - Solubility of Gases in Liquids (Henry's Law)

The solubility of a gas in a liquid is significantly affected by pressure and temperature. The process of dissolution is generally exothermic, meaning solubility decreases as temperature increases according to Le Chatelier's Principle.

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 present above the surface of the liquid or solution.

The most common form of Henry's Law states: The partial pressure of the gas in the vapour phase ($p$) is proportional to the mole fraction of the gas ($x$) in the solution: $p = K_H \cdot x$.

Henry's Law Constant ($K_H$) is a function of the nature of the gas. At a given pressure, the higher the value of $K_H$, the lower is the solubility of the gas in the liquid.

$K_H$ values increase with an increase in temperature, which explains why aquatic species are more comfortable in cold water than in warm water (due to higher dissolved $O_2$).

Applications of Henry's Law include: 1. Increasing solubility of $CO_2$ in soft drinks by sealing the bottle under high pressure. 2. Using Helium to dilute air in scuba tanks to avoid 'bends' caused by $N_2$ bubbles. 3. Explaining Anoxia at high altitudes where low partial pressure of $O_2$ leads to low oxygen concentrations in the blood.