Vapor Pressure: Molecular Size - Methanol and Ethanol
Methanol and ethanol have similar structures and similar intermolecular forces, but differ in molecular weight. Which has the higher vapor pressure?
When methanol is injected, the methanol rises to the top and vaporizes. The mercury column is depressed to 634 millimeters. (Errata, the voiceover erroneously states that reading is 640 millimeters.) When ethanol is injected, the ethanol rises to the top and vaporizes. Here, the mercury column is only depressed to 688 millimeters.
Methanol has the higher vapor pressure because its molecular weight is less than ethanol and so its intermolecular forces are less than ethanol's.
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