August 24, 2019, 02:46:22 PM
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Topic: Aluminium Chloride Melting Point vs Sublimation Point  (Read 400 times)

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Offline hairygorillaz

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Aluminium Chloride Melting Point vs Sublimation Point
« on: March 28, 2019, 12:21:48 PM »
I have a quick question about AlCl3. I'm wondering if there is a reason why the sublimation point is lower than the melting point. Also, once the compound has been sublimed, how can the melting point be determined?

Offline mjc123

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Re: Aluminium Chloride Melting Point vs Sublimation Point
« Reply #1 on: March 28, 2019, 01:55:35 PM »
The vapour pressure of the solid reaches 1 atm at a temperature below the melting point. Draw a phase diagram with the triple point at a pressure > 1 atm, and then draw a line at P = 1 atm.

Offline hairygorillaz

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Re: Aluminium Chloride Melting Point vs Sublimation Point
« Reply #2 on: March 28, 2019, 10:22:38 PM »
Arh. So am I right to say sublimation temperature and melting points (at least here) are theoretical constructs and not something that is measured? Because I was wondering how at 1atm, you could measure the melting point when the compound would have sublimed.

Offline AWK

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Re: Aluminium Chloride Melting Point vs Sublimation Point
« Reply #3 on: March 29, 2019, 03:46:28 AM »
If you look well on the internet, you will find information that AlCl3 melts at a pressure of 2.5 atm. Unfortunately, this information is not available in English wikipedia.
AWK

Offline mjc123

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Re: Aluminium Chloride Melting Point vs Sublimation Point
« Reply #4 on: March 29, 2019, 05:38:44 AM »
Quote
So am I right to say sublimation temperature and melting points (at least here) are theoretical constructs and not something that is measured?
No, I was merely trying to help you visualise how the melting point could be above the sublimation point. Both are measured quantities (m.p. at pressures > 1atm).

Offline hairygorillaz

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Re: Aluminium Chloride Melting Point vs Sublimation Point
« Reply #5 on: March 29, 2019, 07:27:20 AM »
If you look well on the internet, you will find information that AlCl3 melts at a pressure of 2.5 atm. Unfortunately, this information is not available in English wikipedia.

Ah. I tried looking in the CRC Handbook and I didn’t find this piece of information.

Offline hairygorillaz

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Re: Aluminium Chloride Melting Point vs Sublimation Point
« Reply #6 on: March 29, 2019, 07:27:54 AM »
Quote
So am I right to say sublimation temperature and melting points (at least here) are theoretical constructs and not something that is measured?
No, I was merely trying to help you visualise how the melting point could be above the sublimation point. Both are measured quantities (m.p. at pressures > 1atm).

I see. Thanks a lot! :)

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