[3415]

mixture of two liquids X and Y at 100。C has a vapor pressure of 250torr. If the vapor pressure of X and Y are 140torr and 300 torr respectively, what is the mole fraction of each in the solution and also in the vapor above that solution?

I have the answer of the first question.
A*140 torr +(1-A)*300 torr=250 torr
A=0.313 and B=0.687 B=1-A

I am confused by the vapor pressure of the solution and the vapor pressure above the liquid.
Could you help me?
Thanks a lot~

[3415]

oh, I got it. Is that the vapor pressure above the liquid is the vapor pressure of the pure solvent at that temperature?

[MrTeo]

The pressure of the vapor above the solution (which is the vapor pressure of the solution, according to the definition of vapor pressure) is already given by the text: it's 250 torr and the first part of the problem is right.

Now to solve the second one you have to consider that the liquid with the higher vapor pressure is more volatile than the other. If the two vapor pressures are equal, vapor has the same composition of the solution.

[3415]

thank you very much