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Enthalpy of fusion of aqueous solutions of ethylene glycol

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seanspotatobusiness:
Would the enthalpy of fusion of a mixture of water and monoethylene glycol be a simple summation of the fractions of enthalpy of fusion of water and ethylene glycol that comprise the mixture or would some interaction between the molecules give the mixture a completely different enthalpy of fusion?

I've seen ways to measure it empirically, but I don't own much of the required equipment to do that so it would be nice if it was unnecessary to do so.

Incidentally, with monoethylene glycol being hygroscopic, is there a point at which it would stop absorbing water from the air, if continually exposed to air at a particular relative humidity? If so, at what percentage water/ethylene glycol would it stop absorbing water from the air?

Thanks!

Corribus:

--- Quote from: seanspotatobusiness on August 14, 2022, 02:37:06 PM ---Would the enthalpy of fusion of a mixture of water and monoethylene glycol be a simple summation of the fractions of enthalpy of fusion of water and ethylene glycol that comprise the mixture or would some interaction between the molecules give the mixture a completely different enthalpy of fusion?

--- End quote ---
You would have to account for the interactions between the two substances. You may be able to find experimental data in the literature for different mixtures.


--- Quote ---Incidentally, with monoethylene glycol being hygroscopic, is there a point at which it would stop absorbing water from the air, if continually exposed to air at a particular relative humidity? If so, at what percentage water/ethylene glycol would it stop absorbing water from the air?

--- End quote ---
The amount of absorbed water would depend on the solubility of water in ethylene glycol. You may look up the concept of "partition coefficient". A related concept for air/solvent mixtures is the Henry Law constant.

Enthalpy:
I too expect serious departure from a weighed sum of the enthalpies of fusion. Especially for those two compounds, known and used to make a eutectic.

Yes, published data. It abounds for glycol+water.

Equilibrium with air moisture: I tried for glycerine, and after 15% water was absorbed in the mixture, the mass didn't evolve any more. The process was slow enough (a week for cloth-thin glycerine) that the mass didn't fluctuate with the weather. So for a canister with open tap, you won't see much in years. Only properties very sensitive to water contents, like the conductivity or the viscosity, do change.

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