1. Let us consider a solution of phenol and aniline. Both phenol and aniline form hydrogen bonding interactions amongst themselves.
2. When mixed with aniline, the phenol molecule forms hydrogen bonding interactions with aniline, which are Stronger than the hydrogen bonds formed amongst themselves.
3. Formation of new hydrogen bonds considerably reduce the escaping tendency of phenol and aniline from the solution.
4. As a result, the vapour pressure of the solution is less and there is a slight decrease in volume (∆Vmixing < 0) on mixing.
5. During this process evolution of heat takes place i.e., ∆Vmixing < 0 (exothermic).
6. Examples – Acetone + Chloroform, Chloroform + Diethyl ether
