Vapor Pressure

The vapor pressure,P_vp, of a liquid or solid is the pressure of the compound’s vapor (gas) in equilibrium with the pure, condensed liquid or solid phase of the compound at a given temperature. Vapor pressure, which is temperature dependent, increases with temperature.

    The vapor pressure of chemicals varies widely according to the degree of intermolecular attractions between like molecules: The stronger the intermolecular attraction, the lower the magnitude of the vapor pressure. Vapor pressure and the Henry’s law constant should not be confused.Vapor pressurerefers to the volatility from the pure substance into the atmosphere; the Henry’s law constantrefers to the volatility of the compound from liquid solution into the air. Vapor pressure is used to estimate the Henry’s law constant.