HENRY'S LAW (SOLUBILITY OF GAS IN LIQUIDS)

HENRY'S LAW (Solubility of gas in liquid)

Henry's law states that at 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 liquid or solution.

If we use the mole fraction of a gas as a measure of solubility, then the law can be said that 

the mole fraction of gas in the solution is proportional to the partial pressure of the gas over the solutions.

or

Henry's law states that the partial pressure of the gas in vapour phase (p) is proportional to the mole fraction of the gas (x) in the solution. Mathematically 

     p = K_Hx

K_H is the Henry's  law constant.

The plot of the partial pressure of HCl vs. its mole fraction in a solution of cyclohexane is given below.

K_H is the function of nature of gas therefore it has different values for different gases at same temperatue.

It is very clear from the above equation that higher the value of K_H at a given pressure, the lower is the solubility of the gas in the liquid.

Generally the K_H value increases with increase in temperature. This is the reason that aquatic species are more comfortable in cold waters than in the warm water.

Applications of Henry's law.

1. The concept is used in the production of soft drinks and soda water. The solubility of carbon dioxide increases at high pressure.
2. To avoid the condition of bends and toxic effects of high concentrations of nitrogen in the blood, the tanks carried by scuba divers are filled with air diluted with helium.
3. At higher altitudes the solubility of oxygen in the blood and tissues of people reduces due to low partial pressure of oxygen which causes climbers to become weak and unable to think clearly (anoxia).

For complete notes of Class 12 Chemistry chapter 2 click here

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