given that Pben is 94.6 torr and Ptoluene is 29.1 torr, where the total vapor pressure is 72 torr.
The answers are Pben 0.85 and Ptol 0.15 but i dont' understand how they came up with the answer. Could someone help with a walk through? Thanks!
Ian
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Your in Luck.
so first thing to note is that this is a two component raoult's law problem. Therefore we will need to use these equations.
Ya*P=Xa*Pa.sat
Yb*P=Xb*Pb.sat
Pa.sat and Pb.sat are saturated pressures (vapor partial pressures) which are given to you in the question
Ya and Yb are mole fractions in the liquid phase ( which we aren't given and will not need)
Xa and Xb are mole fraction in the vapor phase ( which we are trying to find)
let a be toluene and b benzene
We know that sum of mole fraction must equal one.
so Ya + Yb = 1
when we rewrite raoult's law using algebra, we see that:
P= Xa*Pa.sat + Xb*Pb.sat
Now there is a problem because we have 2 unknowns. This is really easy to deal with since its two component.
Here we can also say that summation of mole fraction for vapor phase must equal 1.
Xa +Xb=1
so
Xb=1-Xa
then we plug this back into main equation
P= Xa*Pa.sat + (1-Xa)*Pb.sat
solve for Xa then solve for Xb
Jane
can you post the work you have done so that it can be seen where you get stuck