[oompaloo]

Does anyone know how to figure out the vapor composition of an 80% hexane and 20% pentane solution when the vapor is condensed and the liquid below is heated?  Thanks in advance!

[mike]

P_solvent = X_solvent x P^o_solvent   [Raoult's Law]

X = mole fraction of solvent
P = vapour pressure of pure solvent

P_total = P_solvent1 + P_solvent2 [Dalton's Law]

P_total = X_solvent1 x P^o_solvent1 + (1 - X_solvent1) x P^o_solvent2

These equations might help (?)

[oompaloo]

I have those formulas but I have no idea where to find the numbers to plug into those equations???  The only information I have is a solution containing 80% hexane and 20% pentane.  How do you figure out the numbers to plug into the equations???

[mike]

I would have thought you could work out the partial pressure of hexane and pentane for 80% and 20% (0.8 and 0.2 mole fraction) and then the partial pressures would be proportional to the amount of vapour.

[mike]

For example:

mole fraction of solvent 1 in vapour is:

P₁/P_total

P₁/P₁+P₂ = X_solvent1xP^o_solvent1/X_solvent1 x P^o_solvent1 + (1 - X_solvent1) x P^o_solvent2