Is it true that the stronger the intermolecular interactions the higher the vapor pressure?

1 Answer
Oct 28, 2016

The reverse is true. The stronger the intermolecular interaction, the weaker the vapour pressure.


Liquids with strong intermolecular interaction tend to have low vapour pressures, which makes sense intuitively. Water, which has exceptionally strong intermolecular interaction for a molecule of its size (why?), thus has low vapour pressure. Liquids with weaker intermolecular interaction, i.e. for instance the alkane series, tend to have lower boiling points, and necessarily higher vapour pressures.

Here we define boiling point as the temperature at which the vapour pressure of the liquid becomes equal to the ambient pressure, and bubbles of vapour form directly in the liquid. The normal boiling point is specified when the ambient pressure is #1# #atm#, and thus the vapour pressure of the liquid, at its normal boiling point, is #1*atm#.