R.K. Nigam

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.

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.

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.

Thermodynamics of molecular interactions in binary mixtures of non-electrolytes. Molar excess volumes

Abstract Molar excess volumes, V E , for pyridine (A) + α-picoline (B), + β-picoline (B) and + γ-picoline (B) and benzene (A) + toluene (B), + o -xylene (B) and + p -xylene (B) and carbon tetrachloride (A) + n -heptane (B) have been measured dilatometrically as a function of temperature and composition and have been utilized to study B—B and B—B—B interactions in the presence of A via the Mayer—McMillan approach. A model has also been presented to account for these B—B and B—B—B interactions. The V E data at 308.15 K have also been analysed in terms of the “graph theoretical” approach which describes the V E data well for all these mixtures at 308.15 K. The “graph theoretical” approach has further been extended to successfully evaluate V E data for a mixture at any temperature, T 2 , when the V E data at T 1 are known.

Anodic oxidation of niobium in aqueous solution of weak organic acids

Abstract Steady state kinetic data for the anodic growth of films on niobium in 0.1 N oxalic, citric and tartaric acid at different temperatures and current densities (CDs) have been obtained. The breakdown voltage of oxide films on niobium has been found to be within the range 210–290 V in oxalic acid solution, 210–355 V in tartaric acid solution and 220–355 V in citric acid solution. It depends on both CD and temperature. The constants (A and B) of Guntherschulze and Betz for the empirical relation between the ionic CD and the field have been found to depend on the nature of the electrolyte. The constant A is temperature dependent while B is temperature independent. The Tafel slope has been found to be independent of the temperature range studied. Dignams quadratic variation of field with ionic current density was examined critically and φ, the zero field activation energy, C, the dimensionless constant, μ∗, the zero-field activation dipole, W(E), the net activation energy, ω∗, the Morse function parameter and i0, the current density were evaluated. It has been found that μ∗, ω∗ and i0 are temperature dependent whereas φ, W(E) and C are temperature independent. All these parameters depend on the nature of the electrolyte. The quantity W(E) does not depend on CD while φ and C change slightly and μ∗, ω∗ and i0 change markedly with changing CD. An appreciable contribution (22%–28%) of the quadratic term has been observed. Single-barrier theories of ionic conduction are not suitable for the present data.

Thermodynamic and spectroscopic evidence in binary mixtures of nonelectrolytes

Abstract Nigam, R.K. and Aggarwal, S., 1986. Thermodynamic and spectroscopic evidence in binary mixtures of nonelectrolytes. Fluid Phase Equilibria , 26: 181–200. Molar excess enthalpies H E m of 1,2-dichloroethane (1)+pyridine (2), + α-picoline (2),+n-hexane (2), +n-heptane (2), n-heptane (1)+pyridine (2), +α-picoline (2), +γ-picoline (2), aniline (1)+pyridine 92), +α-picoline (2) and +γ-picoline (2) mixtures have been measured calorimetrically at 298.15 and 308.15 K. The data have been examined in terms of the Lacombe and Sanchez theory and the graph theoretical approach. It was found that these were described better by the graph theoretical approach. The NMR studies on 1,2-dichloroethane (1)+α-picoline (2), aniline (1)+pyridine (2) and aniline (1)+γ-picoline (2) mixtures have also been used to lend credence to the nature and extent of interaction in these mixtures.

Excess volumes of mixing of 1,2-dichloroethane and aromatic hydrocarbons

Abstract Excess volumes of mixing, V E , for binary mixtures of 1,2-dichloroethane with benzene, toluene, o − , m − , and p -xylenes have been determined at 308.15 K over the complete composition range. V E is positive for all these mixtures and varies in the order m -xylene > o -xylene > p -xylene > benzene > toluene. The experimental data have been analyzed in terms of the Prigogines average potential cell model coupled with Balescus theory. The calculated V E values do not agree with the corresponding experimental values.

Excess volumes of mixing of aniline + aromatic hydrocarbons

The excess volumes of mixing, VE, of aniline with benzene, toluene, o-xylene, m-xylene and p-xylene have been measured at temperatures 293.15, 298.15, 303.15 and 308.15 K over the whole composition range. The results indicate very weak electron donor–acceptor type interactions in these binary liquid mixtures. The shape and size of the aromatic hydrocarbon are responsible for stretching or breaking of hydrogen bonding in aniline.