Thermodynamic properties of polar fluids from a perturbed-dipolar-hard-sphere equation of state

Based on theoretical results for a system of hard spheres with dipoles, a new equation of state is applied to the correlation of thermodynamic properties for four fluids: argon, ammonia, water and acetonitrile. The reference system has the same dependence on density as that given by the Carnahan-Starling equation, but the coefficients are now functions of temperature through the reduced dipole moment. These coefficients are chosen to match the Padé approximant developed by Rushbrooke, Stell and Hoye for the Helmholtz energy of dipolar hard spheres. The reference system proposed here shows a phase transition for reduced dipole moments greater than 1.9. A simple, empirical perturbation term is added to the reference system to account for induction and dispersion forces. For polar fluids, the equation gives results significantly better than those obtained from conventional cubic equations of state, when using the same limited experimental data for determining equation-of-state parameters.     

Structure and phase behavior of Widom-Rowlinson model calculated from a nonuniform Ornstein-Zernike equation

The second-order integral-equation formalism of [Attard J. Chem. Phys. 91, 3072 (1989); 95, 4471 (1991)], applied previously to one-component hard spheres and Lennard-Jones fluids, as well as to their mixtures, is used to binary Widom-Rowlinson mixtures. Comparison with Monte Carlo simulations of the pair correlation functions and of the demixing phase diagram shows that this method is also quite accurate in the case of highly nonadditive mixtures. Moreover, the results of the second-order theory are compared with previous theoretical predictions. Our interest is also in the calculation of the bridge functions, i.e., parts of the radial distribution functions either not included or simply approximated in the usual theories.     

Application of efficient algorithm for solving six-dimensional molecular Ornstein-Zernike equation

In this article, we propose an efficient algorithm for solving six-dimensional molecular Ornstein-Zernike (MOZ) equation. In this algorithm, the modified direct inversion in iterative subspace, which is known as the fast convergent method for solving the integral equation theory of liquids, is adopted. This method is found to be effective for the convergence of the MOZ equation with a simple initial guess. For the accurate averaging of the correlation functions over the molecular orientations, we use the Lebedev-Laikov quadrature. The appropriate number of grid points for the quadrature is decided by the analysis of the dielectric constant. We also analyze the excess chemical potential of aqueous ions and compare the results of the MOZ with those of the reference interaction site model.     

Corridor of existence of thermodynamically consistent solution of the Ornstein-Zernike equation

We obtain the exact equation for a correction to the Ornstein-Zernike (OZ) equation based on the assumption of the uniqueness of thermodynamical functions. We show that this equation is reduced to a differential equation with one arbitrary parameter for the hard sphere model. The compressibility factor within narrow limits of this parameter variation can either coincide with one of the formulas obtained on the basis of analytical solutions of the OZ equation or assume all intermediate values lying in a corridor between these solutions. In particular, we find the value of this parameter when the thermodynamically consistent compressibility factor corresponds to the Carnahan-Stirling formula.     

Thermodynamic properties for liquid mercury using GMA equation of state

The important known regularities and thermodynamic properties of liquid mercury have been studied based on the average potential energy. Recognised regularities, the linearity of Zeno contour, bulk modulus and secant bulk modulus as functions of temperature, isochors of pressure versus temperature and near linearity of the inverse isobaric expansion coefficient have been investigated, all evaluated using the Goharshadi–Morsali–Abbaspour equation of state. The validity of the equation of state in predicting thermophysical properties is confirmed by a statistical parameter, absolute average deviation, with a maximum value of 0.41, showing excellent agreement with the experiment at temperatures between 293.15 and 323.15?K from low to high pressures.     

The conductivity of dilute electrolyte solutions: Expanded lee and wheaton equation for symmetrical,unsymmetrical and mixed electrolytes

The conductivity equation of Lee and Wheaton is expanded in a power series in the ionic strength I. Different levels of approximation are analyzed and it is shown that for unsymmetrical electrolytes it is necessary to keep the terms I^3/2lnI and I² to maintain the performance of the full equation.     

The Ornstein-Zernike equation, critical phenomena, and the equation of state for liquids and gases

It is shown that the Ornstein-Zernike (OZ) equation has two solutions: the standard one, which depends explicitly on the interaction potential, and a second universal one, resulting from the infinity point of the partition function. It is stressed that there are two pressure components: the standard one and a universal one that is valid over the whole of the phase plane. It is concluded that the universal solution parameters depend in general on definite integrals of functions dependent on the interaction potential. In the vicinity of the critical point, however, the dependence on the interaction potential vanishes; i.e., the solution becomes fully universal. It is shown that in this range of the phase diagram, all results of the theory of critical phenomena (scaling theory) follow from the OZ equation.     

Thermodynamic properties of individual ions, calculated in terms of conception of real thermodynamic properties of individual ions in solutions

Real and chemical thermodynamic characteristics for several ions in mixtures of water with organic solvents of different classes are calculated on the basis of the proposed conception of real thermodynamic properties of individual ions in solutions. This conception is an improved and generalized version of the procedure for describing thermodynamic activity of individual ions in aqueous electrolyte solutions, which was successfully exploited for many years. The offered methodology enables one to determine thermodynamic characteristics of individual ions both in aqueous and nonaqueous electrolytes. The use of the Volta potential differences for determining real and chemical thermodynamic characteristics of individual ions in solutions is validated.     

Thermodynamic interpretation of three-parametric equation; Part I. New from of equation

Thermodynamic interpretation of three-parametric equation connecting conversion degree (a) with temperature (T) was presented. One proved that thermal decomposition process of chemically defined compounds (CuSO₄·5H₂O, PhN(CH₃)₂·HCl) in dynamic conditions for 5 heating rates may be described by transformed three-parametric equation including equilibrium conversion degree. This revised version was published online in July 2006 with corrections to the Cover Date.     

A description of the vitreous state of simple molecular systems with the use of the Ornstein-Zernike equation

It is suggested that a certain function describing microheterogeneity of the structure of vitreous systems can be introduced into the integrand of the Ornstein-Zernike equation. The generalized Ornstein-Zernike equation obtained this way can be used for calculating the thermodynamic parameters of simple molecular systems (in particular, argon) in the vitreous state.     

Comparative studies of calculation methods for activity coefficients of unsymmetrical mixed electrolytes

Several methods for the calculation of activity coefficients for binary mixed electrolytes are compared. Their accuracies are analysed and the reasons for the different degrees of accuracies are given.     

Thermodynamic property predictions with the trebble-bishnoi equation of state

Predictions of thermodynamic properties including second virial coefficients, enthalpies, isobaric heat capacities, speed of sound, and Joule-Thomson coefficients are presented for the Trebble-Bishnoi equation of state. These predictions are compared both to experimental data and to predictions from the Peng-Robinson equation of state. Both equations of state give reasonable and consistent values for all of the above properties.     

Thermodynamic quantities associated with the interaction of xanthosine with metal ions

Potentiometric equilibrium measurements have been made at 25, 35 and 45°C for the combination of anionic species of xanthosine with Cu(II), Ni(II), Zn(II), Co(II), Mn(II), Mg(II) and Ca(II) in a 1:1 ratio of ligand to metal ion. The enthalpy and the entropy changes for the formation of protonated complexes are calculated from temperature coefficient data. The relatively small values of ΔH_f⁰ coupled with a large positive values of ΔS_f⁰ offers an evidence for the role of entropy as the primary factor favouring the formation of the protonated 1:1 metal chelate species of xanthosine in solution.     

Synthesis and optical properties of conjugated dendrimers with unsymmetrical branching

An improved synthetic approach to conjugated monodendrons with unsymmetrical branching structures is reported. Dendrimers containing two or three such conjugated monodendrons are synthesized and their optical properties are studied. Such dendrimers exhibit broad absorptions and very high fluorescence quantum yields, making them promising candidates for applications in molecular-based photonics.     

Thermodynamic modelling of polymer solutions with a modified Staverman equation

A model describing the thermodynamic behaviour of polymer solutions is derived which explicitly accounts for the flexibility of the polymer chains. Based on computer simulations on various lattices it is shown that the flexibility of a polymer chain can be modelled by distinguishing different polymer conformations. Here each conformation is characterized by its corresponding number of external contact sites. The equilibrium between the different conformations is then solved for any polymer concentration and any combination of interaction energies utilizing a modified Staverman equation. The model predictions are in good agreement with the results of the computer simulations which were performed using the simple-sampling and the slithering-snake algorithm. Since the knowledge of the distribution of the conformations of a single polymer chain on an empty lattice is a prerequisite to perform the model calculations, Poisson distribution functions are fitted to the results of the corresponding computer simulations. The generalization of these distribution functions not only facilitates the use of the new model but also allows to model polymers of varying chain stiffness.     

Thermodynamic studies of complex formation of actinyl ions extracted with TBP from hydrochloric and nitric acids

The changes of the free energy, enthalpy and entropy accompanying the extraction of the U/VI/, Np/VI/ and Pu/VI/ by TBP have been determined by the method of extraction chromatography. The results obtained indicate outer-sphere complexation.