vapor pressure

[sanghamitra]

when an evacuated container at constant temperature contains some liquid.some of liquid molecules pass into gaseous state and some of them condenses.when the space above the container is completely filled with liquid molecules it is said to be saturated .At saturation point it cannot accommodate any more liquid molecules.

***** ** It is said that saturated v.p does not depend upon presence of air molecules.But how can saturated vapor pressure doesnot depend on presence of air molecules????

In fact saturated v.p of liquid molecules should decrease because air molecules present will definitely occupy some space and hence the number of liquid molecules present are relatively less than the number of liq molecules in absence of air .Thus the pressure exerted by liquid molecules in presence of air molecules is relatively less than pressure exerted by molecules in absence of air

[vascop]

Its because of Dalton's Law of Partial pressures which says that a gas in a chamber with other gases exerts the same pressure as it would if it occupied the space on its own at the same temperature. This is because the molecules of the individual gases are so far apart that they don't notice each other.

[vascop]

Hello, it's me again. Just to clarify: It's NOT correct to say (as you do) that

"when the space above the container is completely filled with liquid molecules it is said to be saturated .At saturation point it cannot accommodate any more liquid molecules"

What actually happens is that for the given temperature an equilibrium state is reached where the number of molecules leaving the liquid is equal to the number of molecules re-entering the liquid.
That is the definition of saturated vapour pressure.
It doesn't mean that there is no more space for any more molecules. There will in fact be plenty of space - most of a gas is empty space.