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Author: Subject: Azeotropes and eutectic mixtures questions thread.
Neal
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[*] posted on 9-11-2023 at 18:41
Azeotropes and eutectic mixtures questions thread.


Azeotropes are:

2 liquids that mixed together that end up having a new bp.

But, the new bp, is always above or below, the 2 individual liquids bp.

Is it because of a reason, or no 1 has discovered 1 yet? Wikipedia has a list of over 50 azeotropes, so it must be some law.

Then, eutectic mixtures are somewhat the freezing point equivalent of 2 liquids.

But, is it that the "new fp" is always below, the lower of the 2 liquids fp? It can't be above, or in-between?

3. I'd like to know, if snow could form a eutectic mixture with a something that has a higher freezing point than it, so you can have some sort of snowman above 32 F? Candlewax, I heard.

4. But what is the fp of azeotropes, and bp of eutectic mixtures supposed to be? Relative to the individual fp and bp.

Wikipedia's big list of azeotropes only shows bp, not fp.

5. And you know, it would be an amazing coincidence, if something can be both an azeotrope, and a eutectic mixture, at the same time!
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[*] posted on 11-11-2023 at 07:16


Quote: Originally posted by Neal  
Azeotropes are:

2 liquids that mixed together that end up having a new bp.

But, the new bp, is always above or below, the 2 individual liquids bp.

Is it because of a reason, or no 1 has discovered 1 yet? Wikipedia has a list of over 50 azeotropes, so it must be some law.

Yes, it is for reasons.
Quote: Originally posted by Neal  

Then, eutectic mixtures are somewhat the freezing point equivalent of 2 liquids.

But, is it that the "new fp" is always below, the lower of the 2 liquids fp? It can't be above, or in-between?

Eutectic point is always a freezing point minimum. Maxima are different things (unlike azeotrope, which includes both minima and maxima). Also, not all freezing point minima are eutectics.
Then again, both eutectics and azeotropes need to be local extrema.
Quote: Originally posted by Neal  

3. I'd like to know, if snow could form a eutectic mixture with a something that has a higher freezing point than it, so you can have some sort of snowman above 32 F? Candlewax, I heard.

Then you heard wrong. Eutectics are by definition lower melting point. Then again, you have a lot of crystal hydrates - but which of them are fit for snowmen?
Quote: Originally posted by Neal  

4. But what is the fp of azeotropes, and bp of eutectic mixtures supposed to be? Relative to the individual fp and bp.

No special rule for that.
Quote: Originally posted by Neal  

Wikipedia's big list of azeotropes only shows bp, not fp.

5. And you know, it would be an amazing coincidence, if something can be both an azeotrope, and a eutectic mixture, at the same time!

Indeed.
Note that neither azeotropes nor eutectics generally correspond to small integer compositions. Freezing point maxima do.
Azeotrope compositions vary with pressure, so when you have an azeotrope coincidentally close but not exactly at the eutectic composition, you could change the pressure to make the azeotrope exactly equal. Though this kind of coincidence would be an obstacle to separation... you would rather like to break such a coincidence.
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