Raoult’s law
- Raoult’s law establishes a quantitative relationship between the partial vapour pressure and mole fraction of a solution.
- This law is only for liquid-liquid solution.
- 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 0x
Where p0 is the vapour pressure of pure component at the same temperature.
- Thus, for component 1, p1 = p1 0 x1 and for component 2 p2 = p20 x
- 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,
pi0 = 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
