Aqueous solutions of nonelectrolytes

The liquid state is one of the three principal states of matter and arguably the most important one, the main reasons being the following: (I) the majority of chemical synthesis reactions are liquid-state reactions; (II) separation processes, such as distillation, extraction, and fractional crystallization, are based on vapor–liquid equilibria, liquid–liquid equilibria, and solid–liquid equilibria, respectively, all involving multicomponent mixtures/solutions; (III) when focusing on water as solvent, we note that it is the most abundant substance on the surface of the earth, and being the principal constituent (about 70% by weight) of all living organisms, it is essential for life as we know it. Thus, it is not surprising at all that experimental as well as theoretical work on nonelectrolyte solutions in general, and on aqueous solutions of nonelectrolytes in particular, have held prominent positions in (bio-)physical chemistry for more than a century. The insights thereby gained have contributed decisively to build the formal structure of chemical thermodynamics and have paved the way for the development of practically useful real-solution models needed in chemical engineering. In this review, first the thermodynamic formalism relevant for solubility studies as well as a critical discussion of some popular approximations will be presented concisely. Estimation methods for auxiliary quantities, such as virial coefficients and partial molar volumes at infinite dilution, will be briefly indicated, followed by a summary of rational strategies for data reduction and data correlation. Finally, a few eclectically chosen results obtained for dilute aqueous solutions of nonelectrolytes will be linked to hydrophobic effects, which are generally accepted to play an important role in a wide variety of biological processes.     

Hydration of nonelectrolytes in binary aqueous solutions

Literature data on the thermodynamic properties of binary aqueous solutions of nonelectrolytes that show negative deviations from Raoult’s law due largely to the contribution of the hydration of the solute are briefly surveyed. Attention is focused on simulating the thermodynamic properties of solutions using equations of the cluster model. It is shown that the model is based on the assumption that there exists a distribution of stoichiometric hydrates over hydration numbers. In terms of the theory of ideal associated solutions, the equations for activity coefficients, osmotic coefficients, vapor pressure, and excess thermodynamic functions (volume, Gibbs energy, enthalpy, entropy) are obtained in analytical form. Basic parameters in the equations are the hydration numbers of the nonelectrolyte (the mathematical expectation of the distribution of hydrates) and the dispersions of the distribution. It is concluded that the model equations adequately describe the thermodynamic properties of a wide range of nonelectrolytes partly or completely soluble in water.     

The structure of solutions of nonelectrolytes

Journal of Structural Chemistry -     

Surface thermodynamic functions of dilute solutions of methylcyclohexanols in ethylene glycol

Surface thermodynamic functions (surface entropy, surface enthalpy, and surface composition) of dilute solutions of 2-, 3-, and 4-methylcyclohexanol in ethylene glycol were obtained using surface tension measurements at various temperatures. Surface excess values and surface mole fractions were obtained from Gibbs equation and extended Langmuir model respectively. The results show that all methylcyclohexanols are surface active in ethylene glycol. The lyophobicity of solutes decreases with increasing temperature. The presence of a maximum point in the surface entropy diagram in all systems is explained by the formation of clathrate-like solvates at the surface of these systems.     

Evaluation of thermodynamic functions relative to cavity formation in aqueous solutions

The results of calculation of free Gibbs energy and enthalpy of cavity formation were described using the Scaled Particle and Sinanoglu's theories.

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Zusammenfassung Mittels der zitierten Theorien wurden die Resultate der Berechnung der freien Gibbs'schen Energien und Enthalpien für die Hohlraumbildung beschrieben.

     

Prediction of excess enthalpies for ternary aqueous solutions of nonelectrolytes

The excess enthalpiesH _xy ^E of ternary aqueous solutions of nonelectrolytes are used to test the possibility of making predictions for ternary solutions from the properties of the binary solutions only. Two methods are proposed: one is based on the empirical rule (h _xx ·h _yy )^1/2=h _xy . Another leads to the numerical prediction of the overallH _xy ^E . Both are successful for most of the pairs of solutes for whichH _x ^E ,H _y ^E >0.     

Adsorption from solutions of nonelectrolytes on solid adsorbents

Summary We have calculated the individual adsorption isotherms from solutions of chloroform-carbon tetrachloride on three adsorbents using only the data on adsorption from solutions.     

Boiling temperatures and excess thermodynamic functions of 2-propanol-n-alkyl propanoate solutions

Boiling temperatures of five binary systems are measured by ebuliometer in the pressure range of 5.333?C101.3 kPa. The compositions of equilibrium vapor phases in the systems are calculated using the constructed saturated vapor pressure isotherms as a base. The excess Gibbs energies, excess enthalpies, and excess entropies of solutions are calculated from our data on liquid-vapor equilibria. Regularities in the changes of phase equilibria and thermodynamic properties of solutions with the composition and temperature of the system are established. Vapor-liquid equilibria in the systems are described by the Wilson and NRTL equations.     

Exploring the structural,mechanical and thermodynamic properties of Ti-V solid solutions

Although Ti-V based high-temperature alloys are used in aerospace engine, rocket engine and hot sections, the structure and mechanical properties of Ti-V alloys remains controversy. To explore the correlation between structural and mechanical properties, we apply employed the DFT method to study the phases stability, mechanical and thermodynamic properties of Ti-V solid solution. Two Ti-V solid solutions: Ti(V)_ss solid solution and V(Ti)_ss solid solution are discussed. Two Ti-V solid solutions are thermodynamic stability. In particular, the Ti-V solid solution prefers to form V(Ti)_ss solid solution, in while the V(Ti)_ss solid solution remains cubic structure. Furthermore, the Ti(V)_ss solid solution is a mechanical instability. However, the V(Ti)_ss solid solution is a mechanical stability. Here, the bulk modulus, shear modulus and Young's modulus of V(Ti)_ss solid solution are 136.9, 23.5 and 66.7 GPa. In particular, the bulk modulus of V(Ti)_ss solid solution is higher than the bulk modulus of the pure Ti. In addition, the V(Ti)_ss solid solution shows better ductility compared to the pure Ti and V. Naturally, the stability and mechanical properties of V(Ti) solid solution is related to the Ti-V metallic bond because of the localized hybridization between the Ti(3d) and V(3d).     

Pressure-induced structural and hydration changes of proteins in aqueous solutions

The effects of elevated hydrostatic pressure on four representative proteins, lysozyme, human serum albumin, ubiquitin and RNase A, were investigated by using Fourier transform infrared (FTIR) spectroscopy, by principal component analysis (PCA) and by moving-window two-dimensional (MW2D) correlation analysis. In addition, we revealed the pressure-induced changes of secondary structure elements using curve fitting. With pressure increase, the amide I band shifted to lower wavenumbers, with a transition at 200 MPa, which was indicative of hydration enhancement. Moreover, the pressure-induced behavior of pure water was studied, similar transition pressure was observed with protein in aqueous solution, suggesting that structure change of water around 200 MPa caused a hydration enhancement of protein. Under pressure higher than 200 MPa, the structural changes of the four proteins were obviously different except for the common features shifting to lower wavenumbers with pressure, basically due to the distinct structural differences among them.