vapour phase ( p ) is proportional to the mole fraction of the gas ( x ) in the solution” and is expressed as: p = K H x ( . ) Here K H is the Henry’s law constant. If we draw a graph between partial pressure of the gas versus mole fraction of the gas in solution, then we should get a plot of the type as shown in Fig. .
. Different gases have different K H values at the same temperature (Table . ). This suggests that K H is a function of the nature of the gas.
It is obvious from equation ( . ) that higher the value of K H at a given pressure, the lower is the solubility of the gas in the liquid. It can be seen from Table . that K H values for both N and O increase with increase of temperature indicating that the solubility of gases Fig.
. : Effect of pressure on the solubility of a gas. The concentration of dissolved gas is proportional to the pressure on the gas above the solution. Fig.
. : Experimental results for the solubility of HCl gas in cyclohexane at K . The slope of the line is the Henry’s Law constant, K H . increases with decrease of temperature.
It is due to this reason that aquatic species are more comfortable in cold waters rather than in warm waters. Henry’s law finds several applications in industry and explains some biological phenomena. Notable among these are: · To increase the solubility of CO in soft drinks and soda water, the bottle is sealed under high pressure. · Scuba divers must cope with high concentrations of dissolved gases while breathing air at high pressure underwater.
Increased pressure increases the solubility of atmospheric gases in blood. When the divers come towards surface, the pressure gradually decreases. This releases the dissolved gases and leads to the formation of bubbles of nitrogen in the blood. This blocks capillaries and creates a medical condition known as bends , which are painful and dangerous to life.