Henry’s law describes the relationship between the pressure of a gas and its solubility in a liquid. It states that the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid.
Mathematically, it can be represented as:
Where:
- is the concentration of the dissolved gas in the liquid,
- is Henry’s Law constant, which is specific to the gas-liquid combination and the temperature,
- is the partial pressure of the gas above the liquid.
Henry’s Law is widely used in various fields such as chemistry, environmental science, and engineering, especially in contexts like gas dissolution in water and the behavior of gases in biological systems.
p = KH x χ
Where, p= partial pressure of gas, χ = mole fraction of the gas in solution,
KH = Henry’s constant which depends upon, temperature, nature of the solvent, nature of the gas.
Henry’s Law can be applied only when:
- Pressure is low and the temperature should be high.
- The gas should not be highly soluble in water.
- The gas should not react with the solvent.
- The gas should not under any association or dissociation in the solvent.
The solubility of gases in liquids typically increases with increasing pressure, according to Henry’s Law. This relationship can be understood by considering the molecular interactions between gas molecules and the molecules of the solvent (liquid).
When the pressure above the liquid increases, more gas molecules are forced into contact with the liquid surface. This leads to more gas molecules dissolving in the liquid phase. Essentially, the higher pressure drives more gas molecules into solution because there are more gas molecules available to interact with the liquid.
Conversely, if the pressure above the liquid decreases, fewer gas molecules are in contact with the liquid surface, resulting in fewer gas molecules dissolving in the liquid phase.
Henry’s Law quantitatively describes this relationship by stating that the concentration of the dissolved gas is directly proportional to the partial pressure of the gas above the liquid. Therefore, as the pressure increases, so does the solubility of the gas in the liquid. However, it’s essential to note that this relationship holds true only for ideal solutions and for gases that do not chemically react with the solvent.
- To increase the solubility of CO2 in soda water and aerated drinks, the bottle is sealed under high pressure.
- To avoid bends and also toxic effects of high concentration of nitrogen in the blood, the cylinders used by the scuba divers are filled with air diluted with 11.7% He, 32.1% oxygen, 56.2% nitrogen.
- When air enters the lungs, partial pressure of oxygen being high, haemoglobin combines with oxygen to form oxyhaemoglobin. Partial pressure of oxygen in tissues is low. Hence, oxygen is released from oxyhaemoglobin which is utilised by the cells.
- Anoxia is felt only due to the low concentration of oxygen in the blood and tissues which occurs at high altitudes, where the partial pressure of oxygen is low.
According to Henry’s Law, The mass of a gas dissolved in a given volume of the liquid at constant temperature is directly proportional to the pressure of the gas present in equilibrium with the liquid.
That’s why to increase the solubility of CO2 in soda water and aerated drinks, the bottle is sealed under high pressure.
Generally, the solubility of gases in liquids decreases with an increase in temperature, as described by Henry’s law.
When a carbonated beverage is opened, the pressure above the liquid decreases, causing the dissolved carbon dioxide gas to come out of solution, forming bubbles and giving the drink its fizz.
Henry’s law is important in scuba diving because it helps explain how nitrogen dissolves in the bloodstream under high pressure at depth and how it can form bubbles in the body during rapid ascents, leading to decompression sickness.
Gases tend to be less soluble in nonpolar solvents because the interactions between gas molecules and nonpolar solvent molecules are weaker compared to the interactions with polar solvent molecules.
One practical application is the extraction of natural gas from crude oil using the principle of Henry’s law. Gas is released from the oil as pressure decreases, and it can then be separated and collected.
The bends, also known as decompression sickness (DCS), is a condition that can occur in scuba divers when they ascend to the surface too quickly after being at depth for an extended period. This condition arises due to the formation of nitrogen bubbles in the body tissues and bloodstream as a result of dissolved nitrogen coming out of solution too rapidly.
To avoid bends and also toxic effects of high concentration of nitrogen in the blood, the cylinders used by the scuba divers are filled with air diluted with 11.7% He, 32.1% oxygen, 56.2% nitrogen.
To avoid bends and also toxic effects of high concentration of nitrogen in the blood, the cylinders used by the scuba divers are filled with air diluted with 11.7% He, 32.1% oxygen, 56.2% nitrogen.
Anoxia is felt only due to the low concentration of oxygen in the blood and tissues which occurs at high altitudes, where the partial pressure of oxygen is low.
As altitude increases, the atmospheric pressure decreases. This decrease in pressure means there are fewer air molecules in a given volume of air. Since oxygen molecules make up a portion of the air, the decrease in pressure results in a lower partial pressure of oxygen. This reduced partial pressure of oxygen means that less oxygen is available for inhalation with each breath.
To mitigate the risk of anoxia and altitude sickness, individuals traveling to higher altitudes should take gradual steps to acclimatize, stay well-hydrated, avoid overexertion, and be aware of the symptoms of altitude sickness. In severe cases, supplemental oxygen or descent to lower altitudes may be necessary to treat anoxia and prevent further complications.
Solubility is equal to the amount of solute dissolved in 100 g of the solvent to form a saturated solution at a given temperature.
