vapor pressure

"Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases (i.e., liquid or solid)." Vapor pressure also a term used to describe the tendancy a liquid has to evaporate; it measures the tendancy of molecules and atoms to escape froma liquid or solid." A liquid's atmospheric pressure boiling point corresponds to the temperature at which its vapor pressure is equal to the surrounding atmospheric pressure and it is often called the normal boiling point." "The higher is the vapor pressure of a liquid at a given temperature, the lower is the normal boiling point of the liquid." The liquids with the highest vapor pressures have the lowest boiling points."For example, at any given temperature, propane has the highest vapor pressure of any of the liquids in the chart. It also has the lowest normal boiling point(-43.7 °C), which is where the vapor pressure curve of propane (the purple line) intersects the horizontal pressure line of one atmosphere (atm) of absolute vapor pressure."




refrence:http://en.wikipedia.org/wiki/Vapor_pressure#Units_of_vapor_pressure