Dipole-dipole forces are typically stronger than dispersion forces, especially in molecules of comparable mass, due to the nature of the interactions involved.
Dipole-dipole forces arise between molecules that have permanent dipoles. This means that in these molecules, there are regions of partial positive and negative charge due to the difference in electronegativity between the atoms. When these polar molecules come close to each other, the positive end of one molecule is attracted to the negative end of another, leading to a stronger interaction.
On the other hand, dispersion forces, also known as London dispersion forces, are weak attractions that occur due to temporary fluctuations in electron density in atoms or nonpolar molecules. These temporary dipoles can induce a dipole in a neighboring molecule, but the resulting attractive force is generally much weaker compared to the permanent dipoles in dipole-dipole interactions.
In summary, while both forces are intermolecular attractions, the strength and nature of dipole-dipole forces make them significantly stronger than dispersion forces in molecules of similar mass. The permanent dipoles create a consistent and strong attraction that is not present in the temporary nature of dispersion forces.