[cherrybarry]

Kinetically, it seems as though you can never have just liquid in a system. You can have superheated gas, gas-liquid at the saturation point, or saturated liquid with gas above it.

But on the Txy diagram or any phase diagram, there is a region where u just have liquid by itself, though you really don't. My question relates specifically to the Txy diagram where u have two components, so there is an "envelope" where the phase transition occurs.

You also have the two Raoult's Law equation where this applies. yP = xP*(T).

As you are cooling from gas to liquid in a system with two consensable species, you move down through the envelope in the Txy diagram, which tells you the fractions of each species in each phase, and if u know total composition, you also know the relative amounts of liquid and gas (lever rule). Once you are on the liquidus line however, the lever rule implies you have 100% liquid and 0% gas...but isn't this not kinetically possible at whatever T and P you are at? There's always some amount of molecules that escape into the gas phase?

If you were to apply Raoult's Law when either T or P is out of range (for example, T is not between the boiling pts of the two pure components), then u end up with negative and mole fractions greater than 1, which is not physical. However, if T is out of range (below the boiling pt of the less volatile component), you should still have some gas but the Txy diagram says u have 100% liquid.

I'm sure it's a conceptual thing I'm missing, or not reading the diagram correctly. It's just a hypothetical that textbooks don't cover or explain well. Like if you had benzene and toluene in a container at 1 atm and 10 degrees C, the Txy diagram says u have all liquid, but u know some gas is still present, and if u apply Raoults Law, you will get negative mole fractions...although physically, that is not the case

[Donaldson Tan]

I'm sure it's a conceptual thing I'm missing, or not reading the diagram correctly. It's just a hypothetical that textbooks don't cover or explain well. Like if you had benzene and toluene in a container at 1 atm and 10 degrees C, the Txy diagram says u have all liquid, but u know some gas is still present, and if u apply Raoults Law, you will get negative mole fractions...although physically, that is not the case

You use Henry's Law. Raoult's Law works if you have only 1 volatile component. Raoult's Law does not apply to this the Toulene-Benzene mixture.