Non-ideal solutions exhibit either positive or negative deviations from Raoult's law. What are these deviations and why are they caused ? Explain with one example for each type.

Explanation

Positive deviations : In this type of solutions, the total vapour pressure is more than that expected from Raoult.s law, `Delta V_( mix)` and `Delta H_( mix)` are always positive.
Examples : acetone + benzene, ethyl alcohol + chloroform.
Negative deviations : In this type of solutions, total pressure for any mole fraction is less than that according to Raoult.s law. For such solutions, `Delta V_(mix)` and `DeltaH_(mix)` are negative.
Examples : benzene + chloroform, water + sulphuric acid.