Raoult ’ s law
Raoult ’ s law
o
Raoult ’ s law establishes a quantitative relationship between the partial vapour pressure and mole fraction of a solution .
o This law is only for liquid-liquid solution . o
o
The law states that for a solution of volatile liquids , the partial vapour pressure ( p ) of each component in the solution is directly proportional to its mole fraction ( x ).
Mathematically , p ∝ x Or p = p 0 x
Where p 0 is the vapour pressure of pure component at the same temperature .
o Thus , for component 1 , p1 = p1 0 x1 and for component 2 p2 = p2 0 x
o Let the solvent be represented by 1 and solute be represented by 2 . At the point when the solute is non-volatile , just the solvent molecules are present in vapour phase and add to vapour pressure .
Let p1 = vapour pressure of the solvent , x1 = mole fraction ,
pi 0 = vapour pressure in the pure state . According to Raoult ’ s law
p1 ∝ x1
And p1 = p1 0 x1
Fig . a plot between the vapour pressure and the mole fraction of the solvent is linear