Why does methanol have a lower boiling point than ethanol?

Methanol ($C{H}_{3}OH$) has a lower boiling point than ethanol ($C{H}_{3}C{H}_{2}OH$) primarily due to differences in molecular size and the resulting intermolecular forces.

While both alcohols are capable of forming hydrogen bonds—which significantly elevate their boiling points compared to nonpolar hydrocarbons of similar mass—the strength of the attractive forces between molecules increases with the size of the molecule. Ethanol possesses a larger hydrocarbon chain than methanol, which contributes to greater molecular weight and increased surface area for intermolecular interactions. Consequently, more energy is required to overcome these collective attractive forces to transition ethanol from a liquid to a gas, resulting in its higher boiling point of 78 °C compared to methanol's 65 °C.1