State Raoult’s law for solutions of volatile liquid components. Taking a suit example, explain the meaning of positive deviation from Raoult’s law.

Answer:

Raoult’s law states that the partial vapour pressure of a component of a solution at a given temperature is equal to the product of the vapour pressure of the pure component at that temperature and its mole fraction in the solution.

Positive Deviation from Raoult’s law: In those non-ideal solutions, when partial pressure of component ‘A’ in the mixture of ‘A’ and ‘B’ is more than that calculated from Raoult’s law. Similarly, the partial vapour pressure of component ‘B’ can be higher than calculated from Raoult’s law. This type of deviation from ideal behaviour is called positive deviation from Raoult’s law, e.g., water and ethanol, chloroform and water, ethanol and CCl₄, methanol and chloroform, benzene and methanol, acetic acid and toluene, acetone and ethanol, methanol and H₂O.
For positive deviation ΔH_mixing > 0.