[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]

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?

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.

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?

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.