Prem P. Singh

Topological aspects of the thermodynamics of binary mixtures of non-electrolytes

Abstract An approach based on the “graph” theory has been evolved to predict molar excess enthalpies, HE, and molar excess volumes, VE, for a number of binary mixtures of non-electrolytes. The calculated HE and VE values compare reasonably well with their corresponding experimental values. The limitations of this approach have also been discussed.

TOPOLOGICAL ASPECTS OF THE EFFECT OF TEMPERATURE AND PRESSURE ON THE THERMODYNAMICS OF BINARY MIXTURES OF NON-ELECTROLYTES

Abstract An approach, employing the concept of molecular connectivity index of the third degree of graph theory, has been developed to evaluate molar excess enthalpy, H E ( T 1 , x ), and molar excess volume V E ( T 1 , x ) of any kind of binary mixture (liquid as well as gaseous) of non-electrolytes, and the calculated H E ( T 1 , x ) or V E ( T 1 , x ) values agree well with their corresponding experimental values. This approach has also been extended to study the effect of temperature and pressure on H E ( T 1 , x ) and V E ( T 1 , x ) data of any kind of binary mixture of non-electrolytes, and the calculated H E ( T 2 , x , P = 1 atm), H E ( T 2 , x , P 2 ≠ 1 atm), V E ( T 2 , x , P 2 = 1 atm) and V E ( T 2 , x , P 2 ≠ 1 atm) values, obtained from H E ( T 1 , x , P = 1 atm) or V E ( T 1 , x , P = 1 atm) data, compare well with their corresponding experimental values. The approach has further been utilized to evaluate specific volumes ν( T 1 , x , P 2 ⪢ 1 atm) of pure compounds as well as their mixtures when ν( T 1 , P = 1 atm) or ν( T 1 , x , P = 1 atm) data are available; the calculated ν( T 1 , x ) and ν( T 1 , x , P 2 ) values again compare well (within 5% at the worst) with their corresponding experimental values.

Topological studies of the molecular species that characterize lower alkanol + methylene bromide mixtures: molar excess volumes and molar excess enthalpies

Abstract Molar excess volumes, V E , and molar excess enthalpies, H E , have been determined at 298.15 and 308.15 K for the binary mixtures of methanol (A) or ethanol (A) with methylene bromide (B). The V E data for these mixtures have been analysed in terms of an approach that employs the graph theoretical connectivity parameters of the third degrees of the A and the B molecular entities to show, for the first time, that (i) in the pure states while methanol exists mainly as cyclic dimers (with perhaps open chain dimers and trimers), ethanol exists mainly as open chain trimers, and that (ii) in the (A+B) mixtures A (= a n ( n = 1 and/or 2))B molecular species characterize these mixtures. The H E data of these (A+B) mixtures have been utilized to understand the energetics of the various interactions that characterize these binary mixtures. These conclusions have further been substantiated with an analysis of the V E - and the H E data of ROH (A) (R = -CH 3 or -C 2 H 5 )+CHX 3 (B) (X = Cl or Br) mixtures.

Molar excess volumes of ternary mixtures of nonelectrolytes

Abstract Molar excess volumes V E ijk of methylenebromide i + pyridine j + β-picoline ( k , cyclohexane ( i ) + pyridine ( j ) + β-picoline( K ), benzene( i )+toluene( j )+1,2-dichloroethane( k ), benzene( i ) + 0 -xylene( j ) + 1,2-dichloroethane( k ) and benzene( i ) + p -xylene( j ) + 1,2-dichloroethane( k ) mixtures have been determined dilatometrically at 298.15 K. The data have been examined in terms of Sanchez and Lacombe theory and the graph-theoretical approach, and it is found that they are described well by the latter. Self- and cross-volume interaction coefficients V jk , V jjk and V jkk , etc., have also been evaluated and the values utilised to study molecular interactions between the j th and k th molecular species in the presence of the i th in these i + j + k mixtures.

Thermodynamics of molecular interactions in aromatic hydrocarbons + o-chlorotoluene mixtures

Abstract Molar excess volumes,VE, molar excess enthalpies,HE and vapour—liquid equilibrium data have been taken at 308.15 K for benzene, toluene, o-, m-, or p-xylene (A) + o-chlorotoluene (B) mixtures. The data have been analysed in terms of some recent approaches of solutions of non-electrolytes. The results suggest that while both Sanchez and Lacombe theory and the ‘graph theoretical’ approaches describe well theVE andHE data, the molar excess Gibbs free energy,GE, data are best expressed by a modified ‘graph theoretical’ approach.

Pyridine—pyridine interactions in binary mixtures of nonelectrolytes: Molar excess volumes

Abstract Molar excess volumes V E for n -heptane (A) + pyridine (B), + α-picoline (B) and + γ-picoline (B), for 1,2-dichloroethane (A) + pyridine (B), + α-picoline (B) and + n -heptane (B), and for aniline (A) + pyridine (B), + α-picoline (B) and + γ-picoline (B), measured dilatometrically as a function of temperature and composition, are utilised to study pyridine (B)—pyridine (B) and α-picoline (B)—α-picoline (B) interactions in the presence of component A via the Mayer—McMillan approach. A model is also presented to account for these B—B interactions. The V E ( T 1 = 308.15 K, x = 0.5) values for all the mixtures are analysed in terms of the “graph-theoretical” approach, which yields a successful description of the corresponding V E ( T 1 , x A ) data. The V E ( T 2 = 298.15 K, x A ) values evaluated from the corresponding V E ( T 1 = 308.15 K, x A ) values (employing the V E ( T 1 = 308.15 K, x A = 0.5) datum alone) also suggest A—B interactions in these binary mixtures.

Topological aspect of the excess enthalpies of binary mixtures of non-electrolytes

Abstract An approach based on the graph theory has been evolved to predict molar excess enthalpies. H E of binary mixtures of non-electrolytes. The calculated H E values compare reasonably well with the corresponding experimental values. The approach has also been successful in predicting H E data for binary mixtures at other temperatures from H E data at two mole fractions at one temperature only.

Thermochemical investigations of associated solutions. 10. Excess enthalpies and excess volumes of ternary acetone + bromoform + n-hexane mixtures

Excess molar vohtmes and excess enthalpies are reported for binary acetone+ n-hexane, bromoform + n-hexane and acetone + bromoform mixtures, and for the ternary acetone + bromofotm+ n-hexane system at 308.15 K. Results of these measurements are used to test the applications and limitations of a newly derived conventional non-electrolyte associated solution model. The genera1 model assumes that the Gibbs free energy, excess volume and excess enthalpy can be separated into a chemical and physical contribution. The chemical interaction term results from the formation of molecular complexes and the physical contribution describes non-specific interactions between the uncomplexed and associated species in solution. Six binary interaction parameters are initially needed to describe all the binary non-specific interactions present. Simplifying approximations and mathematical manipulations reduces the number of binary interaction parameters to only three values. For many years the chemical industry has recognized the importance of thermodynamic and physical properties in design calculations involving chemical separations, fluid flow and heat transfer. The development of flow calorimeters, continuous dilution dilatometers and vibrating-tube densimeters has enabled the experimental determination of excess enthalpies, heat capacities and volumes of non-electrolyte liquid mixtures with convenience and accuracy. The utilization of continuous dilution methods, combined with modern chromatographic head-space sampling techniques, has reduced

Molar excess volumes and molar excess enthalpies of methylenebromide + aromatic hydrocarbon mixtures

Abstract Molar excess volumes V e and molar excess enthalpies H e of binary methylenebromide (i) +benzene. +toluene, and + o−, + m− and + p-xylene (j) mixtures have been determined at 298.15 and 308.15 K. The data have been analysed in terms of recent approaches for solutions of nonelectrolytes, and the results suggest that these mixtures are characterised by specific interactions between the components. Self-volume interaction coefficients Vii Vjj have also been evaluated.

Thermodynamics of aniline + toluene mixtures

Abstract Heats of mixing, HE, of aniline + toluene at 298.15 and 308.15 K and that of aniline + cyclohexane at 308.15 K have been measured over the entire composition range. The excess Gibbs free energies of mixing, GE, for aniline + cyclohexane mixtures at 308.15 K have been obtained from the measured vapour pressure data. The HE and GE values are positive throughout the entire aniline concentration range and HE >GE. The results have been analysed in terms of the Barker and ideal associated model theory of non-electrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AB, AB2, A2B2 and B molecular species describes well (within ±40 J mole−1 at the worst) the general dependence of HE on xB (mole fraction of aniline) over the whole composition range for aniline + toluene mixtures. The equilibrium constants for the various association reactions, along with the enthalpies of formation of various molecular species have also been calculated.