Heat capacity and density of methylpyrrolidone solutions of sodium and potassium perchlorates at different concentrations and 298.15 K

The heat capacity and density of solutions of sodium and potassium perchlorates in N-methylpyrrolidone (MP) at 298.15 K were studied by calorimetry and densimetry. The standard partial molar heat capacities $ \bar C_{p2}^ \circ $ \bar C_{p2}^ \circ and volumes $ \bar V_2^ \circ $ \bar V_2^ \circ of NaClO₄ and KClO₄ in MP were calculated. The standard heat capacities $ \bar C_{pi}^ \circ $ \bar C_{pi}^ \circ and volumes $ \bar V_i^ \circ $ \bar V_i^ \circ of the perchlorate ion in an MP solution at 298.15 K were determined. The results are discussed with allowance for the specifics of solvation in the solutions of the salts under study. The coordination number of the ClO₄⁻ ion in an MP solution at 298.15 K was calculated.     

Calculating the standard values of the heat capacity of alkaline metal ions and iodide ions in a mixed N-methylpyrrolidone-water solvent at 298.15 K

A system of ionic components of [`(C)]<sub>p,i</sub><sup>0</sup>\bar C_{p,i}^0 is proposed for the standard partial molar heat capacities [`(C)]_p2⁰\bar C_{p2}^0 of electrolytes in a mixed N-methylpyrrolidone (MP)-water solvent. The [`(C)]<sub>p,i</sub><sup>0</sup>\bar C_{p,i}^0 values are calculated for Li<sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, Rb<sup>+</sup>, Cs<sup>+</sup>, and I<sup>−</sup> ions in a mixed MP-water solvent at 298.15 K. The individual components of [`(C)]_p,i⁰\bar C_{p,i}^0 values and their dependence on the solvent composition and ion size are considered.     

Structure and electrical properties of oxygen-deficient strontium copper niobate

The transport properties of Sr_5.66 Cu_0.14Nb_2.20 O_11.30 double perovskite, which enters the homogeneity region of (Sr_1-y Cu _y )₆–_2x Nb_2+2x O_11+3x solid solution, are concerned. The total conductivity is differentiated into terms over wide ranges of temperatures and oxygen partial pressures $ p_{O_2 } $ p_{O_2 } in dry and humid atmospheres. When $ p_{O_2 } $ p_{O_2 } is low or high, a test sample has dominant electron transport of n- or p-type, respectively. In air ($ p_{O_2 } $ p_{O_2 } = 0.21 atm), the p-type electron conductivity term increases with temperature elevation. In a humid atmosphere ($ p_{H_2 O} $ p_{H_2 O} = 0.02 atm), a sample is capable of a reversible incorporation of water occlusion from the gas phase; as a result, some proton conductivity term appears and ion transference numbers increase over a wide range of $ p_{O_2 } $ p_{O_2 } values.     

Partial molal heat capacities of aqueous tetraalkylammonium bromides as functions of temperature

Enthalpies of solution have been measured from 5 to 85°C for aqueous tetraethyl- and tetrapropylammonium bromides, and the integral heat method is employed to evaluate for these electrolytes over a wide temperature range. Data taken from the literature have been used to evaluate for aqueous Bu₄NBr over a similar temperature range. These data, along with similar data for Me₄NBr, previously reported, have been used to evaluate absolute ionic heat capacities. While the absolute values agree only qualitatively with two other methods of division, the temperature dependences of the three methods essentially agree up to 65°C. Heat capacities due to structural effects on the solvent, obtained by subtracting the inherent heat capacities of the ions, are extraordinarily positive for all four tetraalkylammonium ions and have negative temperature coefficients, indicating that all four ions, including the tetramethylammonium ion, are structure-making ions.     

Theoretical investigation of some O-nitrosyl carboxylate biologic molecules �� A natural bond orbital study

Theoretical study of several O-nitrosyl carboxylate compounds have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G** basis set. Geometries obtained from DFT calculations were used to perform the natural bond orbital (NBO) analysis. It is noted that weakness in the O₃-N₂ bond is due to $ n_{O_1 } \to \sigma _{O_3 - N_2 }^* $ n_{O_1 } \to \sigma _{O_3 - N_2 }^* delocalization and is responsible for the longer O₃-N₂ bond lengths in O-nitrosyl carboxylate compounds. It is also noted that decreased occupancy of the localized $ \sigma _{O_3 - N_2 } $ \sigma _{O_3 - N_2 } orbital in the idealized Lewis structure, or increased occupancy of $ \sigma _{O_3 - N_2 }^* $ \sigma _{O_3 - N_2 }^* of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital (NHO) of $ \sigma _{O_3 - N_2 } $ \sigma _{O_3 - N_2 } bond orbital. In addition, the charge transfer energy decreases with the increase of the Hammett constants of subsitutent groups.     

Thermodynamics of resolvation of Mg<Superscript>2+</Superscript>, Ca<Superscript>2+</Superscript>, Cd<Superscript>2+</Superscript>, and Cu<Superscript>2+</Superscript> ions in aqueous-ethanol mixtures on the basis of volta potential difference method

The volta potential difference method at 298.15 K was used to determine the real primary medium effect for magnesium, calcium, cadmium, and copper ions, and also the real Gibbs transfer energy of these ions from water into a mixed water ethanol (EtOH) solution. The surface potential value at the nonaqueous solution/gas phase interface $ \Delta \chi _{H_2 O}^{EtOH} $ \Delta \chi _{H_2 O}^{EtOH} was obtained. With account for this value, chemical thermodynamic characteristics of the studied ions in the water-ethanol solvent were calculated and the effect of composition and nature of the mixed solvent on the values obtained was analyzed. The dependence of variation in the thermodynamic characteristics of cation resolvation was established on their crystallographic radius that corresponds to the following sequence: Ca²⁺ < Cd²⁺ < Cu²⁺ < Mg²⁺.     

New approximation for the general temperature integral

A new approximation has been proposed for calculation of the general temperature integral $ \int\limits_0^T {T^m } e^{ - E/RT} dT $ \int\limits_0^T {T^m } e^{ - E/RT} dT , which frequently occurs in the nonisothermal kinetic analysis with the dependence of the frequency factor on the temperature (A=A ₀ T ^m). It is in the following form:

New approximate formulae for the generalized temperature integral

The generalized temperature integral $ \int\limits_0^T {T^m } \exp ( - E/RT)dT $ \int\limits_0^T {T^m } \exp ( - E/RT)dT frequently occurs in non-isothermal kinetic analysis. Here E is the activation energy, R the universal gas constant and T the absolute temperature. The exponent m arises from the temperature dependence of the pre-exponential factor. This paper has proposed two new approximate formulae for the generalized temperature integral, which are in the following forms:

Thermodynamics study of the Cs2SO4-MgSO4-H2O system at the temperature 298.15 K

The Pitzer ion-interaction model has been used for thermodynamics simulation of the ternary system Cs₂SO₄-MgSO₄-H₂O at 298.15 K. The Pitzer ternary mixing parameter $ \psi _{CsMgSO_4 } $ \psi _{CsMgSO_4 } and thermodynamic characteristics for double salt Cs₂SO₄ · MgSO₄ · 6H₂O have been calculated and the theoretical solubilities isotherm has been plotted.     

Oxygen nonstoichiometry and the thermodynamic properties of manganites Ca1 ? x ? ySrxLayMnO3 ? δ

The content of oxygen in Ca_{0.6 − y} Sr_0.4La _y MnO_{3 − δ}, where y = 0 and 0.05, was determined by coulometric titration over the temperature range 650–950°C at oxygen partial pressure in the gas phase varied from 10⁻⁴ to 1 atm. The results were used to calculate the partial molar enthalpy, Δ$ \bar H $ \bar H _O(δ), and entropy, Δ$ \bar S $ \bar S _O(δ), of oxygen in manganites. Changes in the Δ$ \bar H $ \bar H _O(δ) and Δ$ \bar S $ \bar S _O(δ) dependences caused by the introduction of lanthanum are evidence of the formation of local clusters of the double perovskite type in the Ca_0.6Sr_0.4MnO_{3 − δ} matrix.     

The thermodynamic properties and solvation of ammonium bromide,iodide, and nitrate in methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of ammonium bromide, iodide, and nitrate in methylpyrrolidone (MP) were studied calorimetrically and densimetrically at 298.15 K. The standard partial molar heat capacities and volumes (\(\overline {C_{p_2 }^O } \) and \(\overline {V_2^O } \)) of the electrolytes in MP were calculated. The standard heat capacities \(\overline {C_{p_i }^O } \) and volumes \(\overline {V_i^O } \) of the nitrate and ammonium ions in MP were determined. The mean coordination numbers of the NH ₄ ⁺ and NO ₃ ^? ions in a solution in MP at 298.15 K were calculated.     

The compressibility of water-dimethyl sulfoxide mixtures over the temperature and pressure ranges 278–323.15 K and 1–1000 bar

The compressibility coefficients of water-dimethyl sulfoxide (DMSO) binary liquid mixtures were measured over the temperature range 278–323.15 K at pressures from atmospheric to 1000 bar. At these state parameters, the partial molar volumes and partial molar compressibility coefficients $ \bar k_1 $ \bar k_1 and $ \bar k_2 $ \bar k_2 of water and DMSO were calculated. The dependences of the compressibility coefficients of mixtures on mixture composition passed a minimum. The minimum shifted to lower DMSO concentrations as the temperature increased. The dependences contained the inversion region where the k value was independent of pressure. The limiting molar partial compressibility coefficient of DMSO $ \bar k_2 $ \bar k_2 was negative at 278.15 K and increased as the temperature grew.     

Comparison study of adsorption of Cl<Superscript>−</Superscript>, Br<Superscript>−</Superscript>, and I<Superscript>−</Superscript> ions from dimethyl formamide on In-Ga and Tl-Ga electrodes

The adsorption of Cl⁻, Br⁻, and I⁻ ions on the renewable liquid In-Ga and Tl-Ga electrodes from 0.1 M solutions in dimethyl formamide (DMF) is investigated by using the method of differential capacitance measurements. The results are compared with similar data obtained on Hg and Ga electrodes in DMF and with the corresponding data obtained in acetonitrile (AN). It is shown that, in DMF, the adsorption parameters and the series of surface activity of halide ions (Hal⁻) significantly depend on the metal nature. In contrast to Hg electrode, on which the surface activity of halide ions increases in the series: Cl⁻ < Br⁻ < I⁻, on In-Ga, as well as on the Ga electrode, it varies in the reverse order: I⁻ < Br⁻ < Cl⁻, whereas on the Tl-Ga electrode, partially reversed series of surface activity is observed: Br⁻ < I⁻ < Cl⁻. The results are explained within the framework of Andersen-Bockris model. An analysis of experimental results leads to the following qualitative conclusions: (1) on the In-Ga and Tl-Ga electrodes, as well as on Ga electrode, free energy of metal-Hal⁻ interaction ( $ \Delta G_{_{M - Hal^ - } } $ \Delta G_{_{M - Hal^ - } } ) increases in series I⁻ < Br⁻ < Cl⁻; (2) for Cl⁻, Br⁻, and I⁻, $ \Delta G_{_{M - Hal^ - } } $ \Delta G_{_{M - Hal^ - } } ) grows in series Tl-Ga < In-Ga < Ga; (3) an absolute magnitude of $ \Delta G_{_{M - Hal_1^ - } } - \Delta G_{_{M - Hal_2^ - } } $ \Delta G_{_{M - Hal_1^ - } } - \Delta G_{_{M - Hal_2^ - } } (Hal₁⁻, and Hal₂⁻ are any ions of Cl⁻, Br⁻, and I⁻) increases in series Hg < Tl-Ga < In-Ga < Ga; (4) the metal-DMF chemisorption interaction is much stronger than the metal-AN interaction and increases in series Tl-Ga < In-Ga < Ga.     

Heat capacity and density of potassium iodide solutions in mixed N-methylpyrrolidone-water solvent at 298.15 K

The heat capacity and density of potassium iodide solutions in a mixed N-methylpyrrolidone (MP)-water solvent with a low content of the organic component are measured via calorimetry and densimetry at 298.15 K. Standard partial molal heat capacities \(\bar C_{p,2}^ \circ \) and volumes \(\bar V_2^ \circ \) of potassium iodide in MP-water mixtures are calculated. Standard heat capacities \(\bar C_{p,i}^ \circ \) and volumes \(\bar V_i^ \circ \) of potassium and iodide ions are determined. The character of the changes in heat capacity and volume are discussed on the basis of calculating additivity coefficients δ _c and δ _v upon the mixing of isomolal binary solutions KI-MP and KI-water, depending on the composition of the MP-H₂O mixture and the concentration of the electrolyte.     

Volumetric properties of the water-ethylene glycol mixtures in the temperature range 278–333.15 K at atmospheric pressure

Density of the water-ethylene glycol binary mixtures was measured in the entire range of compositions in the temperature range 278–333.15 K (6 values) at atmospheric pressure using a vibration densimeter. Mixtures with low concentrations of ethylene glycol were studied at 15 temperatures in the range of 274–333.15 K. Excess molar volumes V _m ^E , the partial molar volumes of water -V ₁ and ethylene glycol, -V ₂, the coefficients of thermal volume expansion α of the mixture, the partial molar volume coefficients of thermal expansion of water $ \bar V_1 $ \bar V_1 and ethylene $ \bar V_2 $ \bar V_2 were calculated. Excess molar volumes were described using the Redlich-Kister equation. The density ρ of the mixture was found to increase with the increasing ethylene glycol concentration at all temperatures, but at low content of ethylene glycol the dependence ρ = f(T) of the mixture at ∼276.5 K passed through a maximum. The coefficient α increases sharply in the composition range 0 < x < 0.2, in the range 0.5 < x <1 remains almost unchanged, and at T > 277 K is positive for all compositions. The dependences $ \bar \alpha _1 $ \bar \alpha _1 = f (x) and $ \bar \alpha _2 $ \bar \alpha _2 = f (x) are complex in whole temperature range and are characterized by the presence of an extremum. V _m ^E values are negative at all temperatures, and upon increase in the temperature the deviation from ideality decreases (x is the mole fraction of ethylene glycol).     

Estimation of the critical temperature of thermal explosion for azido-acetic-acid-2-(2-azido-acetoxy)-ethylester using non-isothermal DSC

A method for estimating the critical temperatures (T _b) of thermal explosion for energetic materials is derived from Semenov’s thermal explosion theory and the non-isothermal kinetic equation dα/dt=A ₀ T ^B f(α)e^−E/RT using reasonable hypotheses. The final formula of calculating the value of T _b is $ \left( {\frac{B} {{T_b }} + \frac{E} {{RT_b^2 }}} \right) $ \left( {\frac{B} {{T_b }} + \frac{E} {{RT_b^2 }}} \right) (T _b−T _e0=1. The data needed for the method, E and T _e0, can be obtained from analyses of the non-isothermal DSC curves. When B=0.5 the critical temperature (T _b) of thermal explosion of azido-acetic-acid-2-(2-azido-acetoxy)-ethylester (EGBAA) is determined as 475.65 K.     

Kinetics of methoxy-NNO-Azoxymethane hydrolysis in strong acids

The kinetics of methoxy-NNO-azoxymethane (I) hydrolysis in concentrated solutions of strong acids (HBr, HCl, HClO₄, and H₂SO₄) has been investigated by a manometric method. The gas evolution rate is described by the equation corresponding to two consecutive first-order reactions, with the rate constant of the second reaction considerably exceeding the rate constant of the first reaction, i.e., k ₂ {ie17-1} k ₁. The temperature dependences of k ₁ (s⁻¹) in 47.59% HBr in the temperature range from 60 to 90°C and in 64.16% H₂SO₄ between 80 and 130°C are described by Arrhenius equations with IogA= 12.7 ± 1.5 and 13.6 ± 1.4 and E _a = 115 ± 10 and 137 ± 10 kJ/mol, respectively. The parameters of the Arrhenius equation for the rate constant k ₂ for the reaction in 64.16% H₂SO₄ between 80 and 130°C are IogA= 9.1 ± 2.5 and E _a = 91 ± 18 kJ/mol. An analysis of the UV spectra of compound I in concentrated H₂SO₄ shows that I is a weak base $ (pK_{BH^ + } \approx - 6) $ (pK_{BH^ + } \approx - 6) . The rate-determining step of the hydrolysis of I is the attack of the nucleophile on the carbon atom of the MeO group of the protonated molecule of I. The resulting methyldiazene dioxide decomposes via a complicated mechanism to evolve N₂, NO, and N₂O. The pseudo-first-order rate constant k ₁ of the reaction at 80°C depends strongly on the acid concentration and on the type of nucleophile (Br⁻, Cl⁻, or H₂O). The relationship between k ₁ and the rate constant k of the bimolecular nucleophilic substitution reaction (S_N2) is given by the linear equation log$ [k_1 /(C_H + C_{Nu} )] = m^ \ne m*X_0 + \log (k/K_{BH^ + } ) $ [k_1 /(C_H + C_{Nu} )] = m^ \ne m*X_0 + \log (k/K_{BH^ + } ) , where $ C_{H^ + } $ C_{H^ + } and C _Nu are the concentrations of H+ and nucleophile, respectively; X ₀ is the excess acidity; and m ^≠ and m* are coefficients. The Swain-Scott equation log$ (k_{Nu} /k_{H_2 O} ) = ns $ (k_{Nu} /k_{H_2 O} ) = ns , where n is the nucleophilicity factor and s is the substrate constant (s = 0.72), is applicable to the rate constants k of the S_N2 reactions of the protonated molecule of I with Br⁻, Cl⁻, and H₂O.     

Dependence of molecular polarizability on the orientational order in nematic liquid crystals

The dispersion dependences of refractive indices in the visible range were used to obtain experimental values of the Lorentz tensor components L _j and the mean molecular polarizability $ \bar \gamma $ \bar \gamma for five nematic liquid crystals belonging to two homological series. The dependence of L _j components on the homologue number, mesophase temperature, birefringence value, and the orientational order of molecules in the nematic phase and upon a nematic-smectic A phase transition was revealed. The effect of the isotropization of the Lorentz tensors and the local field tensor with decreasing birefringence and molecular polarizability anisotropy Δγ was confirmed. The quadratic dependence $ \bar \gamma $ \bar \gamma (S) on the molecular orientational order parameter S in the nematic phase was found. It was invariant with respect to the nematic-smectic A transition. The dependences $ \bar \gamma $ \bar \gamma (S) and Δγ(S) are explained within molecular statistical theory as consequences of the correlation between orientational and conformational degrees of freedom of molecules. These conformational degrees of freedom are related to the internal rotation of molecular fragments, which affects the electronic conjugation of the fragments and the oscillator strengths of molecular transitions.     

Electrochemical and thermodynamic properties of thulium trichloride in a molten NaCl-KCl-CsCl eutectic

Potentiometric method was used to measure the redox potentials of Tm³⁺/Tm²⁺ in a eutectic melt of sodium, potassium, and cesium chlorides relative to a chlorine reference electrode in the temperature range 823–973 K. The main thermodynamic characteristics of the redox reaction TmCl_2(solution) + 1/2Cl_2(g) ⇆ TmCl_3(solution) were calculate from the conditional standard potentials $ E_{{{Tm^{3 + } } \mathord{\left/ {\vphantom {{Tm^{3 + } } {Tm^{2 + } }}} \right. \kern-\nulldelimiterspace} {Tm^{2 + } }}}^* $ E_{{{Tm^{3 + } } \mathord{\left/ {\vphantom {{Tm^{3 + } } {Tm^{2 + } }}} \right. \kern-\nulldelimiterspace} {Tm^{2 + } }}}^* .