2-component Phase Diagram

[SaintJude]

Do you guys see 2-component phase diagrams in TBR? This came up in Kaplan and they spent a good 2 pages on it, I guess b/c it's the type of phase diagram that would appear in a a difficult passage to trip people up.

It took me a while to understand what was going on.

View attachment phase diagram 1.jpg

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[chiddler]

what's the difference between the two lines?

 

[SaintJude]

you mean the line between the two lines? or the the difference b/w the actual lines?

The line between the two lines indicates the boiling point of the entire solution (the mixture containing both liquids) For this solution, it's 85.

The curved lines show the different composition of the liquid and vapor phase for solution at different temperatures. the Upper curve = composition of vapor. Lower curve= composition of liquid.

So at any of the temperatures shown, one should be able to see how much of component A of will be in vapor phase, and how much of B will be in liquid or vapor. It's pretty cool.

 

[chiddler]

i'm glad you posted this. i haven't seen this graph before.

thanks.

 

[MedPR]

Sorry, I still don't get it..

So this is a mixture of A and B, right? And pure A has a boiling point greater than pure B.

Ok so the point where the two lines intersect all the way on the left is at the BP of pure B, right? And A boils at a hotter temp than B, right? So if you heat it only hot enough to reach the boiling point of B, how can the mol fraction of A be 0.0 in the liquid phase? None of A has boiled off yet since its boiling point is higher...

 

[gettheleadout]

Sorry, I still don't get it..

So this is a mixture of A and B, right? And pure A has a boiling point greater than pure B.

Ok so the point where the two lines intersect all the way on the left is at the BP of pure B, right? And A boils at a hotter temp than B, right? So if you heat it only hot enough to reach the boiling point of B, how can the mol fraction of A be 0.0 in the liquid phase? None of A has boiled off yet since its boiling point is higher...

It's not a change like that, they're just saying in the case that mixture is pure B, the mole fraction is therefore 1.0 and the b.p. is 80.

 

[MedPR]

It's not a change like that, they're just saying in the case that mixture is pure B, the mole fraction is therefore 1.0 and the b.p. is 80.

Oh! Ok thank you, I think I understand it now.

It's just showing the boiling point of all the possible mixtures of A and B including pure A and pure B.

So this is just a graphical expression of Raoult's law?

 

[MrNeuro]

Oh! Ok thank you, I think I understand it now.

It's just showing the boiling point of all the possible mixtures of A and B including pure A and pure B.

So this is just a graphical expression of Raoult's law?

i think tbr has stuff like this too.

 

[MedPR]

i think tbr has stuff like this too.

Yea it might. When I saw "phase diagram" in the OP I was thinking about the ones that show the critical point and triple point. This diagram might be in the gases chapter in TBR.

 

[typicalindian]

Am I the only one who had this graph in my ochem lab class? Pretty sure it's the same...