Question

Define hydrogen bond. Is it weaker or stronger than the van der Waals forces?

Answer 1

A hydrogen bond is defined as an attractive force acting between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule (may be of the same kind). 
Due to a difference between electronegativities, the bond pair between hydrogen and the electronegative atom gets drifted far away from the hydrogen atom. As a result, a hydrogen atom becomes electropositive with respect to the other atom and acquires a positive charge.

\(4^δ-X^{δ-}.......H^{δ+} -X^{δ-}.....H^{δ+}-X^{δ-}\)

The magnitude of \(H-bonding\) is maximum in the solid state and minimum in the gaseous state. 
There are two types of \(H-bonds\) : 
(i) Intermolecular \(H-bond\) e.g., \(HF\), \(H_2O\) etc.
(ii) Intramolecular \(H-bond\) e.g., \(o-nitrophenol\)

Hydrogen bonds are stronger than Van der Walls forces since hydrogen bonds are regarded as an extreme form of \(dipole-dipole\) interaction