Showing papers on "Standard molar entropy published in 2018"

Equilibrium in Protic Ionic Liquids: The Degree of Proton Transfer and Thermodynamic Properties.

Abstract: The degree of proton transfer and thermodynamic parameters of six acetate-based protic ionic liquids (PILs) were measured using nuclear magnetic resonance spectroscopy and calculated by van't Hoff analytical method, respectively. The degree of proton transfer of these PILs at 298 K spread over a large range, which is from 39.6% (1-methylpyrrolidinium acetate, [MpyrH][AcO]) to 94.4% (1-butylimidazolium acetate, [BuimH][AcO]). The calculated standard enthalpy change of the reaction (ΔrHmθ) is from -23.30 to -7.80 kJ mol-1 and the standard entropy change of the reaction (ΔrSmθ) is from -42.70 to -8.07 J mol-1 K-1. The correlation between the degree of proton transfer and aqueous ΔpKa or ΔrHmθ was investigated as well. Furthermore, in some special cases, ΔrSmθ, especially the entropy change of symmetry, also plays an important role in affecting the degree of proton transfer.

Equilibrium in Protic Ionic Liquids: The Degree of Proton Transfer and Thermodynamic Properties B

Abstract: The degree of proton transfer and thermodynamic parameters of six acetate-based protic ionic liquids (PILs) were measured using nuclear magnetic resonance spectroscopy and calculated by van’t Hoff analytical method, respectively. The degree of proton transfer of these PILs at 298 K spread over a large range, which is from 39.6% (1-methylpyrrolidinium acetate, [MpyrH][AcO]) to 94.4% (1-butylimidazolium acetate, [BuimH][AcO]). The calculated standard enthalpy change of the reaction (ΔᵣHₘᶿ) is from −23.30 to −7.80 kJ mol–¹ and the standard entropy change of the reaction (ΔᵣSₘᶿ) is from −42.70 to −8.07 J mol–¹ K–¹. The correlation between the degree of proton transfer and aqueous ΔpKₐ or ΔᵣHₘᶿ was investigated as well. Furthermore, in some special cases, ΔᵣSₘᶿ, especially the entropy change of symmetry, also plays an important role in affecting the degree of proton transfer.

Density and Speed-of-Sound Measurements for Dilute Binary Mixtures of Diethylammonium-Based Protic Ionic Liquids with Water

Abstract: Physicochemical properties of diethylammonium (DEA)-based protic ionic liquids and their aqueous solutions were obtained using experimental measurements of density (ρ) at different temperatures from T = (293.15 to 313.15) K and the speed of sound (w) at 298.15 K. Four DEA-based protic ionic liquids (PILs) with carboxylates as anions were synthesized. The standard entropy (S0) and lattice potential energy (UPOT) for pure PILs were estimated from molecular volumes at 298.15 K obtained using experimental density data. Apparent molar volumes (ϕV), isobaric expansivity (α), isentropic compressibility (βS), and isothermal compressibility (βT) have been obtained for aqueous solutions of PILs using experimental density and speed-of-sound data. These data have been further used to understand the electrostriction and concentration dependence of internal pressure. The Passynski method has been used to estimate concentration-dependent hydration numbers of PILs. The results obtained have been discussed in terms of con...

Thermodynamics of Sr2NiMoO6 and Sr2CoMoO6 and their stability under reducing conditions

Abstract: The values of standard enthalpy of formation at 298.15 K and 1 atm for the double perovskites Sr2NiMoO6 and Sr2CoMoO6, measured by means of drop solution calorimetry, were found to be -2418.1 ± 12.4 and -2422.9 ± 9.6 kJ mol-1, respectively. Heat capacity of Sr2NiMoO6 and Sr2CoMoO6 was measured between 2 and 370 K using relaxation and adiabatic calorimetry, and the enthalpy increments - between 373 and 1273 K using drop calorimetry. Low-temperature magnetic and higher-temperature structural phase transformations in Sr2NiMoO6 and Sr2CoMoO6 were discussed from the thermodynamic point of view. Specific heat (Cp), standard enthalpy (ΔT0H0) and standard entropy (S0) functions were derived from the experimental data for both double perovskites. The values of Cp, ΔT0H0 and S0 at 298.15 K were determined to be 202.31 ± 0.61 J mol-1 K-1, 36.12 ± 0.18 kJ mol-1 and 231.3 ± 1.6 J mol-1 K-1 for Sr2NiMoO6, and 212.66 ± 0.64 J mol-1 K-1, 38.25 ± 0.19 kJ mol-1 and 244.4 ± 1.7 J mol-1 K-1 for Sr2CoMoO6, respectively. Additionally, using the thermodynamic data available, phase diagrams with respect to T and pO2 showing stability limits and decomposition products were calculated for Sr2NiMoO6 and Sr2CoMoO6. Though the cobaltite's stability range is wider than nickelate's both in terms of T and pO2, both complex oxides were found to be stable only at reasonably high temperatures and in oxidizing conditions, and metastable at low temperatures.

Hydrogen bond basicity of ionic liquids and molar entropy of hydration of salts as major descriptors in the formation of aqueous biphasic systems.

Abstract: Aqueous biphasic systems (ABS) composed of ionic liquids (ILs) and conventional salts have been largely investigated and successfully used in separation processes, for which the determination of the corresponding ternary phase diagrams is a prerequisite. However, due the large number of ILs that can be prepared and their high structural versatility, it is impossible to experimentally cover and characterize all possible combinations of ILs and salts that may form ABS. The development of tools for the prediction and design of IL-based ABS is thus a crucial requirement. Based on a large compilation of experimental data, a correlation describing the formation of IL-based ABS is shown here, based on the hydrogen-bonding interaction energies of ILs (EHB) obtained by the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) and the molar entropy of hydration of the salt ions. The ability of the proposed model to predict the formation of novel IL-based ABS is further ascertained.

Inspection for desorption behavior and desorption mechanism of oily sludge by thermodynamics and kinetics analysis

Abstract: In this study, the solvent extraction experiment was investigated to probe the desorption behaviors and desorption mechanism of oily sludge with n-heptane as solvent. Desorption isotherms were analyzed and fitted by Langmuir, Freundlich and Redlich-Peterson equations at different temperatures. Then, the thermodynamics parameters such as standard free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°) were calculated. Based on thermodynamics analysis and calculation, oil was proved to exist in the form of the colloidal dispersion system. In addition, the kinetics was fitted by the pseudo-first-order kinetic model and the pseudo-second-order kinetic model. Kinetic studies showed that desorption process of asphaltenes was restrained severely due to strong interactions between sludge and asphaltenes, and resins played a crucial role in asphaltenes desorption. The desorption mechanism was discussed based on experimental results and further analysis. The solvent effect and carry-over effect were deemed to be crucial to oil desorption. The carry-over effect is generated from electrostatic interactions, hydrogen bonds, electron donor-acceptor and π-π interactions, which was also the essence of asphaltenes desorption.

Physicochemical properties of some hydrophobic room-temperature ionic liquids applied to volatile organic compounds biodegradation processes

Abstract: BACKGROUND Ionic liquids (IL) are an interesting solvent choice for specific industrial applications since physicochemical properties can be fine-tuned by modifying the substituent groups or the cation/anion pair. Hydrophobic IL are considered as green solvents and known to be good absorbents for hydrophobic organic compounds. Given their physicochemical properties an industrial application of such compounds can be conceivable. Classical physicochemical properties such as the density, the viscosity and the surface tension have a strong influence on the fluid dynamics, they were therefore measured and determined. RESULTS The density, viscosity and surface tension of 23 hydrophobic IL at room temperature were measured. These compounds are potential candidates for the absorption and biodegradation of Volatile Organic Compounds in a two-phase partitioning bioreactor. The thermal expansion coefficient, molecular volume, standard molar entropy and lattice energy were determined for each IL using empirical and semi-empirical equations based on the density values. Viscosity values were correlated by the Arrhenius equation. Then, the surface excess enthalpy and surface excess entropy were determined from the surface tension values. CONCLUSION The influence of the presence of different functional moieties (unsaturated bonding, oxygenated and cyanide) and the side chain length in the physicochemical properties of these hydrophobic IL was discussed, since their presence affected directly the density, viscosity and surface tension.

Second Law and Non-Equilibrium Entropy of Schottky Systems-Doubts and Verification.

Abstract: Meixner’s historical remark in 1969 “ it can be shown that the concept of entropy in the absence of equilibrium is in fact not only questionable but that it cannot even be defined” is investigated from today’s insight Several statements—such as the three laws of phenomenological thermodynamics, the embedding theorem and the adiabatical uniqueness—are used to get rid of non-equilibrium entropy as a primitive concept In this framework, Clausius inequality of open systems can be derived by use of the defining inequalities which establish the non-equilibrium quantities contact temperature and non-equilibrium molar entropy which allow to describe the interaction between the Schottky system and its controlling equilibrium environment

Empirical study of physicochemical and spectral properties of CuII-containing chelate-based ionic liquids.

Abstract: The physicochemical properties including melting point, density, viscosity, conductivity, and surface tension as well as spectral properties such as infrared and EPR spectra of the chelate-based ILs [Cnmim][Cu(F6-acac)3] (n = 6, 8, 10, 12, 14) were studied as functions of temperature and chain length. The thermodynamic properties such as the standard molar entropy and crystal energy were estimated by Glasser's theory, the molar enthalpy of vaporization was calculated by Kabo's method, and the ionicity was estimated by the Walden rule. Compared with the common ILs, the chelate-based ILs have larger molecular volume, larger density, smaller crystal energy, poorer ionicity and larger enthalpy of vaporization. The infrared spectra data of the ILs showed a red shift of the C-H bond stretching vibration of the alkyl chain in the cation and the EPR spectra showed that the crystal field of Cu2+ was kept when the chain length was elongated, which indicated the existence of microphase separation in the ILs. This work is helpful in understanding the structure-property relations of chelate-based ILs for further application.

Spectrophotometric, Thermodynamic and Density Functional Studies of Charge Transfer Complex Between Benzhydryl Piperazine and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone

Abstract: The charge transfer complex of benzhydryl piperazine as donor with the π-acceptor 2,3-dichloro-5,6-dicyano-p-benzoquinone has been studied spectrophotometrically in acetonitrile medium at different temperatures. On mixing the donor with acceptor, a reddish brown colored charge transfer complex is formed. Electronic absorption spectra of the complex show charge transfer bands at 587, 546 and 457 nm. The molecular composition of the complex was studied by applying Job’s continuous variation and spectrophotometric titration methods. These results support the formation of the complex in a 1:2 ratio. The Benesi–Hildebrand equation has been applied to compute the formation constant and molecular extinction coefficient. Thermodynamic parameters of the charge transfer complexation reaction (standard entropy, standard enthalpy and standard Gibbs free energy) have been calculated. The results of the spectrophotometric study demonstrated that the charge transfer complex formation is endothermic. The computational studies of the charge transfer complex were performed by using the Gaussian 09 W package of programs. The bond lengths, bond angles, dihedral angles, Mulliken atomic charges, molecular electrostatic potential maps and characterization of the highest occupied molecular orbital and lowest unoccupied molecular orbital surfaces of charge transfer complex were computed.

Adsorption of safranin-O dye by peanut shell-based polyurethane type foam

Abstract: The adsorption of safranin-O dye was performed in batch and continuous column sysytems by polyurethane-type rigid foam produced from peanut shell. In batch system, effects of contact time, initial dye concentration, solution pH and temperature on the adsorption were investigated. In column system, solution flow rate and initial dye concentration effect were studied. Under conditions studied, the adsorption of safranin-O was 95-99% for batch system, and 93-99% for column system. Adsorption isotherm best followed the Langmuir model ( R 2 = 0.986). Adsorption kinetics was in consistent with best the pseudo-second order model ( R 2 values ≥ 0.998). Adsorption was of sponteneous nature and in favor of increasing temperature (i.e. endothermic nature). For example, when the temperature was increased from 20 to 60 ° C, standard Gibbs free energy change ( ΔG ° ) dereased regularitly from -5303 to -8170 J mol -1 . The values of standard enthalpy (Δ H ° ) and standard entropy (Δ S ° ) were estimated as 13.35 kJ mol -1 and 0.64 kJ mol -1 K -1 , respectively. Moreover, FTIR and SEM analyses were done, and the results were interpreated in detail.

Second Law and Non-Equilibrium Entropy of Schottky Systems -- Doubts and Verification

Abstract: Meixner's historical remark in 1969 "... it can be shown that the concept of entropy in the absence of equilibrium is in fact not only questionable but that it cannot even be defined...." is investigated from today's insight. Several statements --such as the three laws of phenomenological thermodynamics, the embedding theorem and the adiabatical uniqueness-- are used to get rid of non-equilibrium entropy as a primitive concept. In this framework, Clausius inequality of open systems can be derived by use of the defining inequalities which establish the non-equilibrium quantities contact temperature and non-equilibrium molar entropy which allow to describe the interaction between the Schottky system and its controlling equilibrium environment.

Synthesis of diethyl carbonate from ethanol through different routes: A thermodynamic and comparative analysis

Abstract: In this study, thermodynamic analysis of various possible synthesis routes of diethyl carbonates (DEC), a benign organic carbonate, was carried out and a comparative analysis was performed. Chemical equilibrium constants at standard conditions were calculated using Gibbs free energy of the system. The Benson group contribution method was used to estimate standard heat of formation and standard entropy change of some raw materials/components like dimethyl carbonate. Variation of heat capacity (Cp) with temperature was estimated for different components from the Rozicka-Domalski model. Variation of chemical equilibrium constants with temperature and pressure was studied for various routes. Synthesis of DEC from ethylene carbonate (EC) was also found to be better considering equilibrium constants at room temperature. The CO2 route was found to be the most unfavourable route for DEC synthesis due to stability of CO2 molecules. Moreover, DEC synthesis through the urea route was found to be best at high temperatures since the equilibrium constants were found to increase exponentially. Experiments were conducted for DEC synthesis using the EC route at two temperatures. Activity coefficients were calculated using the UNIFAC model. Experimentally and theoretically determined chemical equilibrium constant values were found to be similar. PRO/II was also used to minimize Gibbs free energy of the system and estimate the equilibrium constants and the results were comparable with those obtained by the equilibrium constant method and the trend was found to be the same for both the methods.

Thermodynamic properties of tetraphenylantimony 1-adamantanecarboxylate

Abstract: In the present work for the first time, the temperature dependence of the heat capacity $$C_{\text{p}}^{\text{o}}$$ = f(T) of tetraphenylantimony (1-adamantanecarboxylate) was determined in the range 5.6–456 K by methods adiabatic vacuum calorimetry and differential scanning calorimetry. The compound fuses in the range 414–446 K without decomposition, and thermodynamic characteristics of fusion were defined and analyzed. Multifractal treatment of low-temperature heat capacity was made as a result topological structure of the compound was established. The complex of standard thermodynamic functions (enthalpy, entropy, the Gibbs energy) was given for crystal and liquid states in the range from T → 0 to 456 K. Also, standard entropy of formation of a substance in the crystalline state at T = 298.15 K was calculated. Comparison of thermodynamic properties was made for the derivatives of antimony studied in the present work and earlier.

Thermodynamic study of the Ag-Tl-Se system using the EMF method with AG 4 RbI 5 as a solid electrolyte

Abstract: The Ag-Tl-Se ternary system in the composition region Ag2Se-Tl2Se-Se was studied in the temperature range 300–450 K by measuring the electromotive force (EMF) in a concentration cell containing a silver electrode and Ag4RbI5 as a solid electrolyte. A previously constructed solid-phase equilibria diagram of this system that included the ternary compounds AgTlSe, Ag3TlSe2, and Ag7TlSe4 was confirmed. The EMF measurements allowed the partial molar functions $$ \left(\Delta \overline{G},\Delta \overline{H},\Delta \overline{S}\right) $$ of silver in some phase regions of the Ag2Se-Tl2Se-Se subsystem to be calculated. Using the solid-phase equilibria diagram, the potential-forming reactions were defined and the standard thermodynamic functions of formation and the standard entropy values of the ternary compounds mentioned above were calculated. Besides experimental results, data reported in the literature for thermodynamic functions of TlSe as well as the standard entropy values of silver and selenium were used in the calculations. The results of the calculations were compared with relevant data in the literature. The results confirmed that it is possible to study the thermodynamics of silver-containing complex systems using this modified EMF method, even if the system contains a more electropositive component than silver.

The Entropy of Deep Eutectic Solvent Formation.

Abstract: The standard entropies S298°E of deep eutectic solvents (DESs), which are liquid binary mixtures of a hydrogen bond acceptor component and a hydrogen bod donor one, are calculated from their molecular volumes, derived from their densities or crystal structures. These values are compared with those of the components—pro-rated according to the DES composition—to obtain the standard entropies of DES formation ΔfS. These quantities are positive, due to the increased number and kinds of hydrogen bonds present in the DESs relative to those in the components. The ΔfS values are also compared with the freezing point depressions of the DESs ΔfusT/K, but no general conclusions on their mutual relationship could be drawn.