Question

For molecules of comparable mass, why are dipole-dipole forces stronger than dispersion forces?

Answer 1

Both dipole-dipole forces and London dispersion forces are intermolecular forces, which means that they're both forces between different molecules. ... Because London dispersion forces are temporary, they're weaker than the permanent dipole-dipole attractions.

Answer 2

Dispersion forces, otherwise known as induced dipole-induced dipole interactions, polarize a molecule slightly into weak negative and weak positive charges. Then coulombs law dictates their electrostatic attractions. However, in dipole-dipole, these molecules are already polarized permanently and typically of a much larger magnitude than an induced dipole for a molecule of the same molar mass. This means that the electrostatic attractions are significantly stronger than the London Dispersion force's.