intermolecular
As we saw when we studied States of Matter , the driving force for particles in the liquid phase to escape into the gas phase depends on both the temperature and identity of the substance. The vapor pressure of a liquid is a measure of this ability. Specifically, vapor pressure is the pressure exerted by a vapor that is in equilibrium with its solid or liquid phase. For substances with a stronger drive to enter the gas phase, more vapor particles will be present in the same amount of space, resulting in a higher pressure. At a given temperature, the vapor pressures of various liquids depends primarily on the strength of intermolecular attractions between individual particles. Figure below shows the relative vapor pressures of several different substances.