March 04, 2021, 12:48:13 AM
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Topic: decreasing freezing point in solutions as coligative property  (Read 183 times)

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Offline mana

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decreasing freezing point in solutions as coligative property
« on: February 23, 2021, 03:30:23 PM »
hi guys
as you know by adding a nonvolatile solute to water the vapor pressure of the solution decreases and it cause lowering the freezing point too, I can't understand how lowering the liquid vapor pressure effect on freezing point and what is the relationship between the liquid vapor pressure and also solid vapor pressure, I would be very grateful if you could help me about that.
thanks in advance for your help

Offline mjc123

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Re: decreasing freezing point in solutions as coligative property
« Reply #1 on: February 23, 2021, 04:51:27 PM »
The reduced vapour pressure does not "cause" the lowering of the freezing point. Both are consequences of the reduced chemical potential of the solvent in the presence of dissolved solute. This makes the liquid more stable relative to the (pure) solid and vapour, so that the solid  :rarrow: liquid transition is more favourable, and the liquid  :rarrow: vapour transition less favourable.

Offline mana

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Re: decreasing freezing point in solutions as coligative property
« Reply #2 on: March 02, 2021, 02:54:53 PM »
The reduced vapour pressure does not "cause" the lowering of the freezing point. Both are consequences of the reduced chemical potential of the solvent in the presence of dissolved solute. This makes the liquid more stable relative to the (pure) solid and vapour, so that the solid  :rarrow: liquid transition is more favourable, and the liquid  :rarrow: vapour transition less favourable.
Thank you, for your reply, so one more question why the chemical potential of the solution is less than the chemical potential of pure solvent?

Offline mjc123

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Re: decreasing freezing point in solutions as coligative property
« Reply #3 on: March 02, 2021, 03:29:59 PM »
Entropy of mixing (to be very simplistic).

Offline Enthalpy

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Re: decreasing freezing point in solutions as coligative property
« Reply #4 on: Yesterday at 05:21:26 AM »
There must be exceptions as everywhere. I think at enantiomers that crystallize better together. Their mixture supposedly has a higher melting point.

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