Henry ’ s law
Henry ’ s law
o This law is for gas-liquid solution .
o Henry ’ s Law establishes aquantitative relation betweenpressure and solubility of a gasin a solvent . o
o
According to the law at a constant temperature , the solubility of a gas in a liquid is directly proportional to the pressure of the gas .
It can also be stated as - The partial pressure of the gas in vapour phase ( p ) is proportional to the mole fraction of the gas ( x ) in the solution .
o Mathematically , p = KH x where KH = Henry ’ s law constant . o o
o
At same temperature different gasses have different KH
It is a function of the nature of the gas . At a given pressure increasing value of KH implies lower solubility of the gas in the liquid .
Value of KH increases with the increase in temperature therefore solubility of gases increases with decreasing temperature . Due to this reason cold water is more sustainable for aquatic life than warm water .
Problem : H2S , a toxic gas with rotten egg like smell , is used for the qualitative analysis . If the solubility of H2S in water at STP is 0.195 m , calculate Henry ' s law constant .
Solution :
It is given that the solubility of H2S in water at STP is 0.195 m , i . e ., 0.195 mol of H2S is dissolved in 1000 g of water .
Moles of water = 1000g / 18g mol -1 = 55.56 mol
∴Mole fraction of H2S , x = Moles of H2S / Moles of H2S + Moles of water 0.195 / ( 0.195 + 55.56 )= 0.0035
At STP , pressure ( p ) = 0.987 bar According to Henry ' s law : p = KH x ⇒ KH = p / x