Excess Free Enthalpy Research Articles

Methods of investigation study of the compatibility of oligomers and polymers by gas chromatography

A chromatographic method is proposed to determine the compatibility of polymers by measuring excess free energy, enthalpy and entropy of mixing. The method is used to determine several mixtures: polystyrene with polyethylene glycol and polyethylene glycol adipate and several oligomer systems. Compatibility with different component ratios in the mixture was studied for a polystyrene-polyethylene glycol adipate system. It was shown that polystyrene does not mix with both polymers in the temperature range studied. Variations of thermodynamic parameters of oligomer mixtures are similar to those of polymer mixtures.

Thermodynamics of n‐alkane systems and the solution theories of flory and prigogine

AbstractThe partial molar excess free enthalpies and enthalpies as well as the molar excess enthalpies of a number of n‐alkane systems were reexamined within the scope of the polymer solution theory of Flory, Orwoll, and Vrij and that of Prigogine in the version after Delmas, Patterson, and Somcynsky. A semiempirical method was used to obtain characteristic n‐alkane data, which obey the principle of corresponding states. By using these data (instead of those from the partition function after Flory and collaborators), a physically realistic interpretation of the excess free enthalpies over the whole concentration range is possible if the combinatorial contribution is purely athermal in nature. Both theories give an enthalpy interaction parameter near zero as expected, whereas neither a significant end effect nor an entropic interaction contribution is apparent from the analyses of the excess free enthalpies. The poor results obtained for the partial excess enthalpies and the enthalpies of mixing reflect the inadequacy of the partition functions on which these modern solution theories are based.

Thermodynamic properties of binary mixtures of cyclohexane with cyclic amines or cyclic ethers at 298.15 K

Excess free energies GE and excess enthalpies HE were determined at 298.15 K for the binary systems cyclohexane + cyclic amine: (CH2)nNH (n = 3 to 7) and (CH2)nNCH3 (n = 4, 5). Values of HE were also measured for mixtures of cyclohexane + tetrahydrofuran and + tetrahydropyran.

ON THE PARAMETER-SEEKING METHOD OF LOCAL COMPOSITION EQUATIONS

A computer algorithm is presented to obtain best parameters of local composition equations. The Simplex method is found to be one of the most effective parameterseeking methods. Numerical calculations are illustrated by a simultaneous fit of excess Gibbs free energy and excess enthalpy of mixing data for the ethanol-cyclohexane system using the Wilson, Heil, and NRTL equations, whose parameters are assumed to vary linearly with temperature.

Excess thermodynamic properties of mixtures of Lennard-Jones liquids

The results of Monte Carlo calculations in the isothermal-isobaric ensemble are reported for a series of binary mixtures of Lennard-Jones liquids at zero pressure and a temperature of 115·8 K. In the case of equimolar mixtures comparison is made with the predictions of several recently developed theories of liquid mixtures. Particularly good results for excess Gibbs free energy and enthalpy are obtained from the variational theory of Mansoori and Leland and for excess volume from the one-fluid version of the so-called van der Waals model.

Thermodynamics of the Molten AgCl ‐ RbCl ‐ NaCl System by Electromotive Force Measurements

Electromotive force measurements have been made using the reversible formation cell Partial molar excess free energies, enthalpies, and excess entropies of mixing of have been measured over the entire composition range of the ternary system. Partial properties of mixing of and and integral properties of mixing have been calculated using an analytical solution of the Gibbs‐Duhem equation. The partial properties of and can be explained on the basis of simple considerations of regular solution behavior. The partial properties of , however, cannot be explained in this way.

The Acetone – Acetic Anhydride – Carbon Disulfide System: Surface Tension, Viscosity, and Total and Partial Vapor Pressures

The surface tensions, viscosities, and vapor pressures, total and partial, have been determined as functions of concentration for the following systems: (a) acetone – acetic anhydride; (b) acetone – carbon disulfide; (c) acetic anhydride – carbon disulfide; and (d) pseudo-binary mixtures of (a) and (b), whose compositions lie on a straight line tangential to the plait point of the ternary system.The general behavior of ideal and non-ideal systems, in regard to surface tension and viscosity is discussed. For the system acetone – carbon disulfide, whose vapor phase can be considered ideal, the activities, activity coefficients, excess free energies, enthalpies and entropies of mixing have been obtained from the vapor pressures. The vapor phase of the other three systems contains acetic anhydride which is associated in the vapor state, and for these systems the experimental data are reported without further calculation.

Thermodynamics of Molten Silver Chloride‐Alkali Chloride Solutions by Electromotive Force Measurements

Electromotive force measurements have been made using the reversible formation cell Various aspects of the cell design are discussed. Measurements were of sufficient precision to give the concentration dependence and the magnitude of the excess free energies, enthalpies, and excess entropies of mixing in the systems. The results are discussed in terms of covalent bonding in molten silver chloride. A simple semiquantitative “dual bonding” model is developed in which “ionic” and “covalent” silver coexist.

Monte Carlo calculations of the thermodynamic properties of mixtures of Lennard-Jones liquids

A method for the calculation of thermodynamic functions of binary mixtures from Monte Carlo data is outlined. Values obtained for the excess free energy, volume and enthalpy for a range of binary Lennard-Jones (12-6) liquids are compared with the predictions of three versions of the APM-theory.

Thermodynamics of binary systems containing amines. Part 5.—Alcohols and pyridine

The isothermal vapour pressures and densities of mixtures of pyridine with ethanol, propan-1-ol and butan-1-ol have been measured and used, together with unpublished data for the heats of mixing for the three mixtures, to calculate excess free energies, enthalpies, entropies and volumes of mixing.

Excess thermodynamic functions of some binary non-electrolyte mixtures. I. Measurements of excess Gibbs free energy, enthalpies, and volumes of mixing

Excess thermodynamic functions of some binary non-electrolyte mixtures. I. Measurements of excess Gibbs free energy, enthalpies, and volumes of mixing

The Effect of Adsorptive Properties of the Support Material on RM Values in Gas-Liquid Partition Chromatography

Adsorption effects accompanying gas-liquid partition chromatography were investigated for supporting materials of three types. Two kinds of plots were employed to characterize these effects: logarithm of rational retention volume (xVg) vs. molar composition of the liquid phase and the excess free enthalpy (ΔgE(m)) vs. molar composition of the mixed stationary phase, the second series of plots being derived from the first one. The experimental results formed the basis of an attempt to explain the behavior of solutes chromatographed on supporting materials of various surface areas.

Thermodynamics of zinc-chloride—sodium-chloride molten mixtures by emf measurements

The molten binary mixture ZnCl2-NaCl was studied by means of emf measurements on galvanic cells. In these cells Pyrex glass functions as a sodium inditor electrode. The excess free enthalpy of mixing at 600°C has been calculated from the emf mesurements. The ZnCl2-NaCl mixture shows a stronger negative deviation from ideal mixing behaviour than the corresponding lead chloride and cadmuim chloride mixtures.

Thermodynamics of cadmium-halide—sodium-halide and lead-halide—sodium-halide molten mixtures by emf measurements

Molten binary mixtures CdCl 2NaCl, CdI 2NaI, PbCl 2NaCl, PbBr 2NaBr, and PbI 2NaI are studied by means of emf measurements on galvanic cells. In these cells Pyrex glass functions as a sodium indicator electrode. Excess free enthalpies of mixing at 600°C have been calculated from the emf measurements. The excess free enthalpy of mixing of all five mixtures under consideration is negative. The cadmium mixtures show stronger deviations from ideal mixing behaviour than the corresponding lead mixtures and the absolute value of the excess free enthalpy of mixing increases in the sequence iodide-bromide-chloride. From the free enthalpy data and literature values for the enthalpy of mixing, CdCl 2NaCl has a nearly ideal entropy of mixing, whereas PbCl 2NaCl has an appreciable positive excess entropy of mixing. It is shown that the emf values are consistent with differences in theoretical emf's of formation cells.

Occurrence of a Double Azeotrope in the Binary System Hexafluorobenzene+Benzene

RECENTLY there has been much interest in the thermo-dynamic properties of binary mixtures of aromatic fluorocarbons and aromatic hydrocarbons. Experimental studies of the phase diagrams1,2, excess volumes3 and excess enthalpies4 of mixing can be interpreted by assuming that intermolecular complexing exists between the two components. This complexing is believed to result from charge–transfer interaction, with the fluorocarbon acting as the electron acceptor. The presence of a specific interaction, of this nature has the effect of reducing the magnitude of all the thermodynamic excess functions from their “normal” large, positive values. For example, in the system hexafluorobenzene + cyclohexane where there is little possibility of charge–transfer interaction, the excess free energy, enthalpy, entropy and volume are all large and positive, whereas these functions are all negative in the system hexafluorobenzene + mesitylene where the hydrocarbon is a strong electron donor. The system hexafluorobenzene + benzene is found to occupy an intermediate position.

Statistical thermodynamics of liquid hydrocarbons Part II—Mixtures

The corresponding states theory for liquids consisting of polysegmented molecules is extended to mixtures of paraffinic, olefinic, naphthenic and aromatic hydrocarbons; the previously derived partition function is generalized to yield expressions for the excess free energy, enthalpy and entropy. It is found that the excess enthalpy arises from the change in potential energy of the system which is due to the change in the average potential field acting on the individual segments and from the change in lattice irregularities upon mixing. The excess entropy arises due to (a) the combinatorial term (Flory-Huggins), (b) the change upon mixing of the size of the average volume in which the segments are free to move, and (c) the change in excitation of the external degrees of freedom when the average potential field acting on the segments is changed in the mixing process. Lattice irregularities appear to have a large effect on the excess functions of mixtures whose components are of different hydrocarbon type. Comparison of predicted with experimental results is favorable.

Thermodynamic properties of silver‐tin and silver‐antimony liquid alloys

AbstractThe e.m.f. measurements were made of the liquid silver‐tin and silver‐antimony alloys. The partial and integral molar excess free energies, excess entropies and excess enthalpies of these systems were determined. The liquidus curve of the antimony rich region in the silver‐antimony system was calculated from the present activity data. The experimental results were discussed in terms of the metallic solution theories.

Thermo dynamic Properties of Indium‐Antimony and Indium‐Bismuth Liquid Alloys

AbstractThe e.m.f. measurements were made on the liquid In‐Sb and In‐Bi alloys. The partial and integral excess free energies, excess entropies and excess enthalpies of these systems have been determined. The phase diagrams of these systems are discussed from the obtained data.

The use of binary stationary phases in gas-liquid partition chromatography

The theoretical basis of choice of optimal composition of the binary mixed stationary phase for a given separation problem is described; a number of practical applications is presented. The possibility of the application of binary solvent systems in gas chromatography is considered for the investigation of the energy effect due to deviations from ideality of binary liquid mixtures. In the experimental part a method of calculation of excess free enthalpies of mixing solvents g E ( m) is given, together with an experimental illustration. The values of g E ( m) have been calculated from the deviations from linearity of the relationship log Xk ′ = mixed phase). The values of partition numbers ( k′) determined from retention times have been used for the calculation of partition coefficients ( K) of solutes at column temperature. The results obtained are compared with partition coefficients calculated from other retention data.

Thermodynamic Properties of Liquid Thallium‐Antimony System

AbstractThermodynamic studies of the liquid thallium‐antimonẏ system were made by means of the e.m.f. method. The activities of this alloy system show a negative deviation from Raoult's law. The partial and integral excess free energies, excess entropies and excess enthalpies of this system have been determined. The liquidus curve of the antimony rich side was calculated from the present activity data.