Question #cc2fd

1 Answer
Jul 27, 2017

You may be confused with what vapor pressure is. It took me awhile to understand, too.

Vapor pressure is the equilibrium state change of a #LrightleftharpoonsG#, where the pressure is the pressure of vapor that has vaporized out of the liquid. The liquid's boiling point is when #P_v = P_a#.

The more volatile a liquid, the higher its vapor pressure. Generally, as temperature increases, #P_v# also does. At a molecular level, this is because the liquid particles' average kinetic energy increases enough to break free of the intermolecular forces within the liquid.

When a liquid has a low #P_v#, it vaporizes less readily and thus tends to not vaporize (think honey, or something, compared to an organic solvent). More simply, the pressure of the vapor of the liquid (within a closed system) isn't high and thus there aren't many gas particles that have "evaporated" from the liquid.