Which liquid, methanol or ethanol, has the larger vapor pressure value at room temperature?

Methanol has the larger at room temperature because it has a lower molecular weight when compared with ethanol, which implies it has weaker .

Both methanol (##"CH"_3"OH"##) and ethanol (##"CH"_3"CH"_2"OH"##) have the capacity to form because of the ##"-OH"## group, so from this standpoint there is no difference between the two.

However, the difference comes when the weaker London dispersion forces come into play. Ethanol has a molecular weight of ##"46 amu"##, while methanol has a molecular weight of ##"32 amu"##.

This difference in molecular weight means stronger London dispersion forces in favor of the heavier molecule - ethanol - which in turn translates into a lower vapor pressure.

As a result, the molecule that exhibits weaker intermolecular forces - methanol - will have the higher vapor pressure.

Ethanol's vapor pressure at ##20^@C## is ##"5.95 kPa"##, while methanol's vapor pressure at the same temperature is ##"12.8 kPa"##.

Check out this answer on the topic of vapor pressure and intermolecular forces:

http://socratic.org/questions/how-does-vapor-pressure-related-to-intermolecular-forces