Solubility of a gas in a liquid can also be expressed in terms of its mole fraction in the solution. So, we can also describe Henry’s law as follows:
The partial pressure of gas is directly proportional to mole fraction of the gas in solution. Thus
or P = X
where is the Henry’s Constant for the gas-liquid pair. This relationship shows that a plot of partial pressure of the gas against its mole fraction in the solution is a straight line.
- The values of (at any common temperature) are different for different gases.
- A less soluble gas has higher value of .
- For any gas, the value of increases with temperature. The decrease in the solubility of oxygen in water explains why the aquatic organisms are less comfortable in warm water.
Henry’s law finds many applications in industry. Some such applications are described below:
Soda water is a solution of carbon dioxide gas [CO2(g)] in water. Soda water bottle is sealed when the CO2 gas is under high pressure. Because of high pressure , and low temperature (because it is chilled), a large amount of gas is dissolved in water. As soon as the bottle is opened under normal atmospheric conditions, the dissolved gas escapes out to reach a new equilibrium state required by the lower pressure (the atmospheric pressure). At lower pressure, the solubility of CO2 gas in water decreases.However, if the soda water bottle is left open to air for some time, most of the carbon dioxide escapes out, and it turns ‘flat’.
Maharastra gov Official Book