Isotope Effects of Water in Liquid–Vapor Equilibria on Passing to Water–Non-Electrolyte Solvent

In solutions of non-electrolytes, there is a single network of hydrogen bonds, including molecules of dissolved substances, bound water, bulk water, and hydration shells of molecules in solution. Under certain conditions, there should be correlations between the bulk properties of the liquid mixture and the separation factor of the isotopic forms of water between the liquid and vapor phases. The shift of the isotope equilibrium in the liquid–vapor phase system for water during the transition from water to non-electrolyte solutions is associated with a violation of the degree of bonding and structuredness of the water of the mixed solvent. Using urea solutions as an example, it is shown that this effect can be one of the main ones and can determine the increase in the separation factor of the isotopic forms of water upon passing from water to a solution.