Here's why:

* Intermolecular forces: The strength of intermolecular forces between molecules determines their boiling point. Stronger intermolecular forces require more energy to overcome, leading to a higher boiling point.

* Dipole-dipole interactions: CH3Cl is a polar molecule due to the electronegativity difference between chlorine and carbon. This creates a permanent dipole moment, allowing for dipole-dipole interactions between molecules, which are stronger than the London dispersion forces present in the nonpolar ethane (CH3CH3).

* London dispersion forces: While both molecules exhibit London dispersion forces, these forces are weaker in ethane due to its smaller size and less polarizability.

In summary: The stronger dipole-dipole interactions in CH3Cl, compared to the weaker London dispersion forces in CH3CH3, result in a higher boiling point for chloromethane.