(1) The hydroxyl group in alcohols is highly polar.
The H-atom has partial positive charge and the oxygen atom has partial -ve charge.
The hydroxyl group in ethanol is extensively hydrogen bonded.
(2) Large number of ethanol molecules associated together by intermolecular hydrogen bonding.
The energy required to separate the molecules by breaking hydrogen bond into vapour state is higher.
This results in increasing the boiling point of ethanol.
(3) On the other hand, in ethane (alkane) there is no hydrogen bonding between the molecules.
The molecules of ethane are held together by weak van der Waals forces of attraction.
Hence,
These molecules can be easily separated.
Thus,
Ethanol has higher boiling point than that of ethane.
