João Carlos R. Reis

Isentropic compressibilities : Experimental origin and the quest for their rigorous estimation in thermodynamically ideal liquid mixtures

In this review, attention is initially focused upon the evolution of the Newton-Laplace Equation, that links the measured speed of sound in a fluid in conjunction with its density, to a reliable estimate of its isentropic compressibility κS. Definitions of ideal and excess isentropic quantities are formulated on the premise that the thermodynamic properties of an ideal mixture are mutually related in the same manner as are those of a real mixture or a pure substance. It is shown that both intensive and extensive properties can be derived from the ideal Gibbs energy. Different approaches previously used to calculate ideal isentropic quantities are examined and some subtle errors are identified. The consequences of using conflicting definitions are pointed out. Isentropic pressure derivatives obtained under different conditions and empirical models for estimating the differences between ultrasonic speeds in real and ideal liquid mixtures are discussed.

Aggregative processes in aqueous solutions of isomeric 2-butoxyethanols at 298.15 K

Ultrasound speed measurements across the entire composition range of aqueous mixtures of both isobutoxyethanol (iC4E1) and tert-butoxyethanol (tC4E1) have been made at 298.15 K with a sonic solution monitor that employs a “pulse–echo–overlap” technique. In addition, densities of aqueous mixtures of tC4E1 were determined using a vibrating tube densimeter. These new data were complemented with literature values for densities of aqueous mixtures of tC4E1 and for densities and sound speeds of aqueous mixtures of n-butoxyethanol (nC4E1). In all cases, density values were converted to molar volumes, Vm, and excess molar volumes, VmE. Estimates of the isentropic molar compression, KS,m [= −(∂Vm/∂p)S], and of its excess counterpart, KS,mE, were obtained from the combination of the ultrasound speeds and density values. Data reduction procedures were used to generate consistent sets of values for thermodynamic properties of isomeric amphiphiles with increasing degree of alkyl branching. The graphs for the composition dependence of excess partial molar volumes and isentropic compressions of water show enhanced visual impact. These graphs are used for presenting evidence for identifying the prevailing patterns of molecular aggregation. Segmented-composition models, including a version onto which a mass action component has been grafted, are employed, together with a simplified pseudo-phase model, to analyse the various excess molar quantities. The experimental evidence thus obtained is used to relate the effect of chain branching with the degree of self-aggregation of amphiphiles in aqueous solution. An unexpectedly low self-aggregation among iC4E1 molecules is found and discussed in terms of vicinity to the lower critical solution temperature.

The concepts of non-Gibbsian and non-Lewisian properties in chemical thermodynamics

The concepts of Gibbsian and non-Gibbsian, Lewisian and non-Lewisian thermodynamic variables are explored with respect to the thermodynamic properties of liquid mixtures and solutions. The general structures of equations for isochoric heat capacities, isentropic compressions and isentropic expansions are compared and contrasted. A simple rule is proposed for transcribing non-Gibbsian equations in terms of non-Lewisian partial molar properties. The bases of equations for partial molar isochoric heat capacities, isentropic compressions and isentropic expansions are examined for (i) components of liquid mixtures, and (ii) solute and solvent in solutions together with the properties of solutes at infinite dilution.

Aggregative processes in aqueous solutions of mono- to tetra-ethylene glycol dimethyl ether at 298.15 K

A sonic solution monitor that employs the “pulse-echo-overlap” technique was used to measure ultrasound speeds in binary liquid mixtures of water with mono- to tetra-ethylene glycol dimethyl ether (also known as mono- to tetra-glyme) across their entire composition ranges. In addition, densities of aqueous mixtures of ethylene glycol dimethyl ether (monoglyme) were determined using a vibrating tube densimeter. The new data were complemented with literature values for the densities of aqueous mixtures of di-, tri- and tetra-glyme. All measurements were made at 298.15 K. Densities were converted to excess molar volumes, VEm. Combination of the densities and ultrasound speeds provided estimates of the excess molar isentropic compressions, KES,m. The excess thermodynamic properties were converted to excess partial and apparent molar properties of both components of each mixture. Negative values are generally observed for all of the excess molar properties. Graphs are presented to exhibit the effects of extending the length of the polyether chain. Data analyses have been carried out using different versions of the four-segment model for aqueous mixtures of amphiphile substances, one version of which including a mass action component. At a given composition in the transitional segment, it is found that the investigated excess molar properties become approximately insensitive to the chain length in the glyme molecules. Present and previously reported VEm data have been combined for constructing series showing the effect of replacing successively the hydroxyl hydrogens in ethan-1,2-diol by methyl groups, as well as increasing the number of ethylene oxide units in 2-methoxyethanol. Along these series of aqueous mixtures, negative excess molar volumes are found to increase in magnitude. Limiting partial molar volumes and isentropic compressions are reported for the glymes in water and for water in the glymes.

Apparent and partial ideal molar isentropic compressibilities of binary liquid mixtures

The excess apparent molar isentropic compressibilities of binary liquid mixtures, which are derived from ultrasonic speed measurements, are frequently used to probe the macroscopic effects of intermolecular forces. The composition dependence of the apparent and partial molar isentropic compressibilities of components of ideal mixtures is explored, with special interest being shown in the infinite aqueous dilution limit. Attention is also paid to convenient methods for estimating the effects of solvation and of cosphere overlap in water-rich mixtures. In particular, it is shown that the difference between excess partial molar and excess apparent molar isentropic compressibilities gives a strong indication of the magnitudes of the effects of solute–solute interactions.

Shape effects in the partial molar volume of tetraethylphosphonium and ammonium iodides in six nonaqueous solvents

AbstractDensities of dilute solutions of the electrolytes tetraethylphosphonium iodide and tetraethylammonium iodide in the nonaqueous solvents methanol, ethanol, 1-propanol, 1-butanol, acetonitrile, and 2-propanone were measured at 25°C. Using published values for the Debye-Hückel limiting slopes AV, apparent molar volume data were fitted to the Pitzer equation yielding infinite-dilution partial molar volumes

The quaternisation reaction of phosphines and amines in aliphatic alcohols. A similarity analysis using the isokinetic, isosolvent and isoselective relationships

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Dipole moments of isomeric alkoxyalcohols in cyclohexane. Comparison of Hedestrand and Fröhlich procedures with a new formula

and deviation parameters BV. It is found that the variation in the van der Waals volume of the cationic central atoms is about one half the experimental volume change in 2-propanone solutions, but twice that value in the other five solvents. This finding is interpreted in terms of openness of solute structure and solvent penetration. Parameter BV for each salt is shown to be solvent dependent. An interesting approximate linear variation between AV and BV parameters is suggested by the data. This empirical relationship would entail correlation of short- and long-range interionic interactions in solution.