# Chemical Forums

## Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Calicum on June 09, 2012, 02:12:16 AM

Title: [General Chemistry 2] What is the composition of the vapor of a pentane-hexane s
Post by: Calicum on June 09, 2012, 02:12:16 AM
Vapor Pressures at 25C
Pure pentane 511 torr
Pure hexane 150 torr

Pentane mole fraction in the vapor =
Hexane mole fraction in the vapor =

I don't seem to understand why my answer is wrong.

My work:

Ptot = X1P1 + X2P2

where Ptot is the vapor pressure of the mixture, X1 is mole fraction of the first component, P1 is the vapor pressure of the pure first component, X2 is mole fraction of the first component, and P2 is the vapor pressure of the pure first component. Notice too that:

X1 + X2 = 1.00

Plug in a solve

Ptot -> 427 = 511X1 + 150X2 X2=1-X1,
substitute:
427 = 511X1 + (1-X1)(150 torr)
427 = 361X1 + 150 277 = 361X1
X1=0.767, pentane mole fraction
X2=0.232, hexane mole fraction
Title: Re: [General Chemistry 2] What is the composition of the vapor of a pentane-hexane s
Post by: Calicum on June 09, 2012, 03:06:58 AM
Nvm I got.  ;D