# Vapor pressure in equilibrium

1. Mar 8, 2005

### filou

Hi
I have difficulties with a problem that my teacher gave in assignement. Teh teacher said it was a bit higher than our level but I think it far above what I am able to do! so here it is :

The vapor pressure in equilibrium with pentane-hexane solution at 25°C has a mole fraction of pentane equal to 0.15 at that temperature. What is the mole fraction in the solution?

Up to now I found that the vapor pressure of pentane is 511 torr and the one of hexane is 150 torr. I think that I should use Raoult's law but my attempts were not concluant... I hope someone will be able to answer my question.

2. Mar 12, 2005

### Gokul43201

Staff Emeritus
$$P^o (P) = 511~,~~P^o (H) = 150$$

$$P(P) = \chi (P.solution) * P^o (P)= 0.15P(tot)$$

$$=>~0.15P(tot) = \chi (P)* 511$$

$$And~0.85P(tot) = (1 - \chi(P))*150$$

Last edited: Mar 12, 2005