Standard Thermodynamic Quantities Research Articles

Molecular Properties of Monoaminergic Catecholamines in Water.

Three neurotransmitters belonging to catecholamines (dopamine, noradrenaline, adrenaline) and related α-amino acids (DOPA and tyrosine) were studied by quantum-chemical ab initio and DFT calculations using B3LYP and DLPNO-CCSD(T) methods in water. In addition to the three canonical forms, zwitterionic forms were also investigated, each in three oxidation states (molecular cation L+, electroneutral molecule L0, and molecular anion L-). Each species was subjected to geometry optimization followed by vibrational analysis. Electronic properties (adiabatic ionization energy, electron affinity, chemical hardness, molecular electronegativity, electrophilicity index, dipole moment, electric polarizability, and quadrupole moment) and standard thermodynamic quantities (inner energy, entropy, enthalpy, and Gibbs energy) were evaluated, which allows the absolute oxidation and reduction potentials to be calculated. The absolute reduction potential (ARP) was found to correlate with the electrophilicity index ω along a straight line. Moreover, in addition to the standard expression for the absolute redox potential using reaction Gibbs energy, an approximation based on ionization energy and/or electron affinity was also tested. The main finding is that dopamine is a much weaker oxidizing agent with the ARP = 0.99 V relative to tyrosine with ARP = 1.38 V for canonical structures in water. This is also true for the zwitterionic structures in water: for dopamine ARP = 0.63 V is much lower relative to tyrosine with ARP = 1.31 V. The protonated form (DOPAH+) has the highest ARP = 2.02 V. Prediction of the redox potentials is an important factor influencing antioxidant (EC50) and/or antireductant activity. Based on 16 molecular properties for 20 molecules (320 entries), advanced statistical methods (cluster analysis, principal component analysis, pair-correlation) reveal that several groups of similarity exist: {dopamine-noradrenaline}, different from {adrenaline-DOPA-(tyrosine)} and zwitterionic forms of {dopamine-noradrenaline-adrenaline}.

Effect of Solvation on Glycine Molecules: A Theoretical Study.

Ab initio calculations of HF+MP2 and DFT-B3LYP quality have been used in calculating the molecular geometries and properties of neutral and charged molecules of glycine in amino acid as well as zwitterionic forms. A traditional set of molecular descriptors has been enriched by the molecular chemical potential, expressed via the Mulliken electronegativity, and Pearson's chemical hardness. In the global energy minimum, the complete vibrational analysis allowed evaluating the standard Gibbs energy and related thermodynamic quantities.

Toward Native Hardwood Lignin Pyrolysis: Insights into Reaction Energetics from Density Functional Theory

Lignin is one of the three structural components of lignocellulosic biomass and the only renewable source for sustainably producing aromatic chemicals. Despite lignin’s promise for targeted valorization to fine chemicals, fuels, and polymer composites, a major roadblock is an ambiguity associated with its molecular structure. Due to the lack of an established molecular structure, all types of computational studies from reaction mechanism to reaction energetics are performed with model lignin compounds. Among several thermochemical conversion techniques, lignin pyrolysis has been an active research area for both experimental and computational investigations. Historically, computational studies on the pyrolysis of lignin have mainly been limited to dimeric or trimeric models using electronic structure methods. Very recently, model oligomers up to the size of decamers have been studied with density functional theory (DFT) calculations. While these studies used very simplified models to study lignin’s pyrolysis behavior, theoretical investigations on a more realistic lignin structure are warranted to advance its state-of-the-art. To address this, we have modeled a native hardwood lignin polymer consisting of 20 repeating units, including all three monolignols, i.e., guaiacyl (G), syringyl (S), and p-hydroxy coumaryl (H) units, and multiple types of linkages, i.e., β-O-4, 4-O-5, β–β, and β-5. This more realistic molecular model for the wild-type poplar lignin is based on a proposed lignin structure reported in a previous experimental study. The initial stage in lignin pyrolysis involves the homolytic cleavage of β-O-4 linkages present in lignin. The activation energy for homolysis of this linkage is considered to be slightly greater than the bond dissociation enthalpy (BDE) required to cleave it. We used a composite method using molecular mechanics-based conformational sampling and quantum mechanically based density functional theory (DFT) calculations to determine the reaction energetics for this reaction, which indicates the activation energy required for the early stage of lignin pyrolysis. In addition, we calculated standard thermodynamic properties for all species, including enthalpy of formation, heat capacity, entropy, and Gibbs free energy of formation as a function of temperature. This study provides the reaction energetics and standard thermodynamic quantities that could be used in kinetic and reactor modeling for biomass conversion. Additionally, these predictions would be particularly helpful in advanced-generation biorefinery, where hardwoods can be used as a potential feedstock. Moreover, the predictions reported in this study will benefit further computational studies and cross-validation with pyrolysis experiments, ultimately contributing to solving the puzzle of the structural ambiguity of lignin.

Effect of N-Methyl-pyrrolidone (NMP) on the Equilibrium Solubility of Meloxicam in Aqueous Media: Correlation, Dissolution Thermodynamics, and Preferential Solvation.

Meloxicam is an analgesic and anti-inflammatory drug widely prescribed in current therapeutics that exhibits very low solubility in water. Thus, this physicochemical property has been studied in N-methyl-pyrrolidone (NMP)–aqueous mixtures at several temperatures to expand the solubility database about pharmaceutical compounds in aqueous–mixed solvents. The flask-shake method and UV–vis spectrophotometry were used for meloxicam solubility determination as a function of temperature and mixture composition. Several cosolvency models, including the Jouyban–Acree model, were challenged for equilibrium solubility correlation and/or prediction. The van’t Hoff and Gibbs equations were employed here to calculate the apparent standard thermodynamic quantities for the dissolution and mixing processes of this drug in these aqueous mixtures. Inverse Kirkwood–Buff integrals were employed to calculate the preferential solvation parameters of meloxicam by NMP in all mixtures. Meloxicam equilibrium solubility increased with increasing temperature, and maximal solubilities were observed in neat NMP at all temperatures. The mole fraction solubility of meloxicam increased from 1.137 × 10–6 in neat water to 3.639 × 10–3 in neat NMP at 298.15 K. The Jouyban–Acree model correlated the meloxicam solubility in these mixtures very well. Dissolution processes were endothermic and entropy-driven in all cases, except in neat water, where nonenthalpy- nor entropy-driven was observed. Apparent Gibbs energies of dissolution varied from 34.35 kJ·mol–1 in pure water to 7.99 kJ·mol–1 in pure NMP at a mean harmonic temperature of 303.0 K. A nonlinear enthalpy–entropy relationship was observed in the plot of dissolution enthalpy vs dissolution Gibbs energy. Meloxicam is preferentially hydrated in water-rich mixtures but preferentially solvated by NMP in the composition interval of 0.16 < x1 < 1.00.

Multi-orbital Hubbard model with infinite-range coulomb coupling

In this paper, we study the role of degeneracy in the Hubbard model featuring infinite-range Coulomb coupling. We put forward its exact solution for any dimension alongside analytical expressions for the one-dimensional (1D) lattice, thus generalizing the solution proposed by Hatsugai and Kohmoto for a single orbital. The ground-state phase diagram is also addressed against the particle density, interaction strength, and orbital number. We show that increasing the orbital number and/or the Hund’s hole coupling favors the phases associated to aligned spins within orbitals. Standard thermodynamic quantities in the grand canonical ensemble are further evaluated in 1D.

Increasing the Equilibrium Solubility of Meloxicam in Aqueous Media by Using Dimethyl Sulfoxide as a Cosolvent: Correlation, Dissolution Thermodynamics and Preferential Solvation

Meloxicam is widely prescribed as an analgesic and anti-inflammatory drug in human therapeutics. Owing the very low aqueous solubility of meloxicam, this property has been studied in dimethyl sulfoxide (DMSO)-aqueous solvent systems at several temperatures from 273.15 to 313.15 K to expand the solubility database about analgesic drugs in mixed solvents. The flask shake method followed by ultraviolet-visible (UV-vis) spectrophotometry analysis were used for meloxicam solubility determinations. A number of cosolvency models, including the Jouyban–Acree model, were challenged for solubility correlation/prediction of this drug in these mixtures. The van’t Hoff and Gibbs equations were employed to calculate the apparent standard thermodynamic quantities relative to dissolution and mixing processes. The inverse Kirkwood–Buff integral method was employed for calculating the preferential solvation parameters of meloxicam by DMSO in the mixtures. Meloxicam solubility increases with increasing temperature and maximum solubilities are observed in neat DMSO at all temperatures studied. Dissolution processes were endothermic in all cases and entropy-driven in the composition interval of 0.40 ≤ x1 ≤ 1.00. A nonlinear enthalpy–entropy relationship was observed in the plot of enthalpy vs. Gibbs energy for drug transfer processes. Meloxicam is preferentially solvated by water in water-rich mixtures but preferentially solvated by DMSO in the composition interval of 0.21 &lt; x1 &lt; 1.00.

Solubility isotherms determination of the H3BO3 + CsCl + H2O system at T = (273.15, 298.15, 323.15, 348.15 and 363.15) K and thermodynamic modeling

The construction of a comprehensive thermodynamic model for boron-containing salt brine is important. However, the general lack of the solubility of H3BO3 + salt + H2O ternary systems makes it difficult to determine model parameters involving boron species. Here, we systematically determined the solubility isotherms of the H3BO3 + CsCl + H2O system at T = (273.15, 298.15, 323.15, 348.15 and 363.15) K. There are three solubility branches corresponding to H3BO3(cr), CsCl(cr) and a novel adduct in the system. The determined composition of the adduct is 2H3BO3·3CsCl. Moreover, the single crystal structure of 2H3BO3·3CsCl is solved, suggesting that H3BO3 molecules keep it native plane-triangle structure, but the O atoms coordinate to the Cs ion. We modeled these ternary solubility isotherms using the Pitzer-Simonson-Clegg (PSC) model implemented in the ISLEC program. With the help of the model, a complete polythermal phase diagram of the system was constructed for the temperature range from 250 K to 373.15 K. The determined standard thermodynamic quantities of 2H3BO3·3CsCl(cr) from the model are ΔfGmΘ = − 3182.26 kJ∙mol−1, ΔfHmΘ = − 3496.19 kJ∙mol−1, SmΘ = 485.85 J∙K−1∙mol−1, Cp,mΘ = 320 J∙K−1∙mol−1, respectively.

Solubility, correlation, dissolution thermodynamics and preferential solvation of meloxicam in aqueous mixtures of 2-propanol

Background: Meloxicam is a powerful analgesic and anti-inflammatory drug widely prescribed by physicians in current therapeutics. Because of the very low aqueous equilibrium solubility of meloxicam, this property has been studied in {2-propanol + water} mixtures from (293.15 to 313.15) K to expand the solubility database about pharmaceutical compounds in mixed solvents useful for homogeneous liquid dosage forms design. Methods: Flask shaken method and UV-vis spectrophotometry were used for meloxicam solubility determinations. Jouyban-Acree model was challenged for solubility correlation. The van’t Hoff and Gibbs equations were employed here to calculate the respective apparent standard thermodynamic quantities for the dissolution and mixing processes, namely Gibbs energy, enthalpy, and entropy. In addition, the inverse Kirkwood-Buff integrals were employed to compute the preferential solvation parameters of meloxicam by 2-propanol in the mixtures. Results: Meloxicam solubility increases with temperature arising and maximum solubilities are observed in the mixture of x1 = 0.70 at all temperatures. Jouyban-Acree model correlates the meloxicam solubility very well. Dissolution processes were endothermic in all cases and entropy-driven in the interval 0.20 ≤ x1 ≤ 1.00. Non-linear enthalpy–entropy relationship was observed in the plot of enthalpy vs. Gibbs energy exhibiting negative but variant slopes in the composition region 0.00 &lt; x1 &lt; 0.40 and variant negative and positive slopes in the other mixtures. Meloxicam is preferentially solvated by water in water-rich mixtures, it is apparently solvated by water in 2-propanol-rich mixtures, but it is preferentially solvated by 2-propanol in the composition interval of 0.19 &lt; x1 &lt; 0.78. Conclusion: Solid-liquid equilibrium of meloxicam in {2-propanol + water} mixtures has been studied at several temperatures as a contribution to preformulation studies of homogeneous liquid pharmaceutical dosage forms based on this drug.

Synthesis and Thermodynamic Investigation of Energy Materials in the Ag-Te-Cl System by the Solid-State Galvanic Cells

Discoveries of new energy materials with unique properties and wider thermal stability ranges enable sustainable developments toward a low-carbon society. In this work, phase stabilities and thermodynamic properties of selected compounds in the Ag-Te-Cl system with potential application as energy materials have been critically reviewed and experimentally investigated. Based on the literature data on phase formations in the AgCl-Ag2Te-Te part of the Ag-Te-Cl system and the results of electromotive force (EMF) measurements in this work, formations of the Ag19Te6Cl7, Ag10Te4Cl3, Ag5Te2Cl, and Ag23Te12Cl compounds below 500 K were established. The EMF measurements were performed in carefully built galvanic cells with positive electrodes prepared from finely ground mixtures of pure substances Ag, Te, and AgCl. Based on the temperature dependences of the EMF of the cells, the standard thermodynamic quantities of the ternary compounds of the Ag-Te-Cl system were experimentally determined for the first time.

Non-analyticity of the Correlation Length in Systems with Exponentially Decaying Interactions

We consider a variety of lattice spin systems (including Ising, Potts and XY models) on mathbb {Z}^d with long-range interactions of the form J_x = psi (x) e^{-|x|}, where psi (x) = e^{{mathsf o}(|x|)} and |cdot | is an arbitrary norm. We characterize explicitly the prefactors psi that give rise to a correlation length that is not analytic in the relevant external parameter(s) (inverse temperature beta , magnetic field h, etc). Our results apply in any dimension. As an interesting particular case, we prove that, in one-dimensional systems, the correlation length is non-analytic whenever psi is summable, in sharp contrast to the well-known analytic behavior of all standard thermodynamic quantities. We also point out that this non-analyticity, when present, also manifests itself in a qualitative change of behavior of the 2-point function. In particular, we relate the lack of analyticity of the correlation length to the failure of the mass gap condition in the Ornstein–Zernike theory of correlations.

THERMODYNAMIC PROPERTIES OF SILVER-CONTAINING COMPOUNDS OF THE Ag–Fe–Sn–S SYSTEM OBTAINED BY LOW-TEMPERATURE SOLID-STATE SYNTHESIS

The existence of the AgFeS2 and Ag2FeS2 compounds in the equilibrium concentration space of the Ag–Fe–S system was established by the EMF method. Investigations were performed in the electrochemical cells (ECCs) of the type (−) С | Ag | SЕ | R(Ag+) | PЕ | С (+), where C is the inert electrode (graphite), Ag is the negative (left) electrode, SE is the solid electrolyte, PE is the positive (right) electrode, R(Ag+) is the region of Ag+ diffusion into PE. Ag2GeS3 glass was used as the solid-state electrolyte with purely Ag+ ionic conductivity. The SnS2–FeS2–Ag2FeS2 (A) phase region of the Ag–Fe–Sn–S system is formed with the participation of three-component compounds. The cross-sections AgFeS2–Ag2FeSnS4, AgFeS2–Ag2FeSn3S8, and AgFeS2–SnS2 carry out the division of (A). Spatial position of the two-phases FeS2–AgFeS2, AgFeS2–Ag2FeS2 and three-phases AgFeS2–Ag2FeSn3S8–SnS2, AgFeS2–Ag2FeSnS4–Ag2FeSn3S8 regions of (A) regarding the point of silver was used to write the equations of the overall potential-forming reactions. Reactions were realized in the positive electrodes of ECCs. PE at the stage of the cell preparation is a well-mixed composition of finely ground (particle size ~5 μm) of the compounds Ag2S, FeS, FeS2 and Ag2S, FeS, FeS2, SnS2 in two- and three-phases regions of (A), respectively. The ratios of compounds in PE of ECCs were determined from the equations of the overall potential-forming reactions in respective phase regions. The decomposition of the metastable set of binary compounds and the synthesis of the equilibrium set of phases were carried out in the nanoscale region of the PE of ECC in contact with SE, i.e. in the R(Ag+) region. The Ag+ ions displaced from the left electrode to the right one for thermodynamic reasons act as nucleation centers for the equilibrium compounds. The process of forming the equilibrium set of phases in the R(Ag+) region for the particle size of the metastable phase mixture ~5 μm and Т=580 K took less than 72 h. The linear dependencies of EMF vs T of ECCs with PE of two- and three-phases regions were established in the ranges of (455–519) K and (450–514) K, respectively. Based on these dependencies, the standard thermodynamic quantities of the AgFeS2, Ag2FeS2, Ag2FeSnS4, and Ag2FeSn3S8 compounds were experimentally determined for the first time. The reliability of the established equilibrium sets of phases that provide the potential-forming reactions in ECCs was confirmed by the coincidence of the calculated and literature values of the Gibbs energy of the Ag2FeSnS4 and Ag2FeSn3S8 compounds.

Sorption of Lanthanum(III) and Neodymium(III) from Concentrated Phosphoric Acid by Strongly Acidic Cation Exchange Resin (SQS-6)

The feasibility of using a macroporous strongly acidic cation exchange resin (SQS-6) as an adsorbent for lanthanum(III) and neodymium(III) from phosphoric acid medium, >4.0 M, was administered using batch and column techniques. Different parameters affecting the sorption of these metal ions such as v/m ratio, acid concentration and the metal ion concentration were separately investigated. The results indicated that the sorption process is relatively fast, reaching equilibrium state within 10 min. Influence of temperature on the equilibrium distribution values was also studied to evaluate the changes in standard thermodynamic quantities where the results indicated that the sorption is endothermic and the process is spontaneous associated with increasing the randomness of the system. The adsorption results of the studied metal ions were found to obey Langmuir isotherm model over the entire studied concentration range. The recovery of La(III) and Nd(III) from the loaded resin was performed with 1.0 M citric acid at pH 4.0. The breakthrough capacity of La(III) and Nd(III) was found to be 33.55 and 17.30 mg/g, respectively. The experimental data resulting from column technique were followed Thomas and Yoon-Nelson models.

Enthalpies of acid dissociation of l-carnosine in aqueous solution

The enthalpies of l-carnosine interaction with solutions of hydrochloric acid have been measured by calorimetric method in the presence of NaCl at 298.15 K and ionic strength as high as 0.25, 0.50 and 0.75 mol dm−3. The enthalpies of acid dissociation have been determined from the obtained data. The effect of a background electrolyte concentration on the dissociation enthalpy of peptide has been considered. Standard thermodynamic quantities (ΔdisH°, ΔdisG°, ΔdisS°) of the acid dissociation of the dipeptide in aqueous solutions have been determined on the basis of the obtained thermochemical results and available data on the acid dissociation constants corrected for the zero-order ionic strength. Ability to acid dissociation of amino acids in a free state is compared with those for amino acid residues involved in the dipeptide linkage. The alteration of acidity has been connected with variation in hydration of reactivity centers.

Solubility and thermodynamics of vitamin C in binary liquid mixtures involving water, methanol, ethanol and isopropanol at different temperatures

Abstract Vitamin C also known as ascorbic acid is an important compound for different fields of knowledge and applications. The development of separation processes and reaction media requires experimental information concerning solid-liquid equilibrium of the organic acid in different pure substances and mixtures. With the intention of raising solubility data, this research aims to perform a study of phase equilibrium involving vitamin C in mixtures formed by water/ethanol, water/isopropanol, methanol/ethanol, methanol/isopropanol and ethanol/isopropanol. The experiment was conducted throughout the molar composition range of the binary solution at the temperatures of 293.15 K, 303.15 K, 313.15 K and 323.15 K. The Jouyban-Acree model was applied in order to correlate the experimental solubility data and the adjustable parameters were calculated as a function of temperature. The experimental results were applied to thermodynamic relations to determine standard functions of dissolution. The increase of temperature leads to a larger amount of dissolved vitamin C. The solubility is also dependent on the solution concentration and that is interconnected with the dielectric constant of the binary solution. The Jouyban-Acree model is able to correlate the experimental data satisfactorily and the standard thermodynamic quantities of dissolution agree with the interpretation of the behavior experimentally observed.

Calibration of phase field parameters demonstrated on kinetics of a shrinking single grain

The phase field method is frequently employed to simulate evolution of rather complex microstructures. In order to accurately describe the real kinetics of a specific material system, the phase field parameters must be calibrated to standard thermodynamic quantities such as interface mobilities or interface energies. This letter presents a convenient method, based on thermodynamic modelling of shrinking of a single grain embedded in single crystal (matrix), how to calibrate the phase field parameters. It also shows, how the required thermodynamic quantities can be met by proper rescaling of a phase field simulation carried out for given phase field parameters.

Study of Complex Formation between Kryptofix 21 with La3+, Y3+ and Ce3+ Cations in Some Binary Mixed Non-Aqueous Solvents Using the Conductometric Method

The complexation reactions between La3+, Y3+ and Ce3+ cations with the macrocyclic ligand, kryptofix 21, were studied in methanol-acetonitrile (MeOH-AN) and methanol-methylacetate (MeOHMeOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most solvent systems, the kryptofix 21 forms a 1: 1 [M: L] complex with La3+, Y3+ and Ce3+ metal cations, but in the case of Y3+ cation in pure methylacetate, in addition of formation of a 1: 1 [ML] complex, 1: 2 [ML2] and 1: 3 [ML3] complexes are formed in solution. In the case of Ce3+cation, a 1: 1 [ML] and also a 1: 2 [ML2] complexes are formed in this solvent system at all studied temperatures. The electrical conductance data in acetonitrile, show that a 1: 1 [ML] and also a 1: 2 [ML2] complexes are formed between the ligand and La3+ and Ce3+ metal cations at different temperatures. The stability constants of the 1: 1 [ML] complexes were determined using the conductometric data and a computer program, GENPLOT. A non-monotonic relationship was observed between logKf of the 1: 1 complexes with the composition of the binary solvent solutions which was discussed in term of solvent-solvent interactions and also preferential solvation of the metal cations and the ligand in solutions. The selectivity order of the ligand for the metal cations in MeOH–AN and MeOH–MeOAc binary solvent solutions, at 25°C was found to be: Y3+ > La3+ > Ce3+ and La3+ > Y3+ > Ce3+, respectively. The values of the standard thermodynamic quantities (ΔHc° and ΔSc°) for formation of the 1: 1 complexes were obtained from temperature dependence of the stability constans of the complexes and the results show that the thermodynamics of the complexation reactions between kryptofix 21 and La3+, Y3+ and Ce3+ cations, is affected by the nature and composition of the mixed solvents systems.

Classical mutual information in mean-field spin glass models

We investigate the classical Renyi entropy S_n and the associated mutual information I_n in the Sherrington-Kirkpatrick (S-K) model, which is the paradigm model of mean-field spin glasses. Using classical Monte Carlo simulations and analytical tools we investigate the S-K model on the n-sheets booklet. This is obtained by gluing together n independent copies of the model, and it is the main ingredient to construct the Renyi entanglement-related quantities. We find a glassy phase at low temperature, whereas at high temperature the model exhibits paramagnetic behavior, consistent with the regular S-K model. The temperature of the paramagnetic-glassy transition depends non-trivially on the geometry of the booklet. At high-temperatures we provide the exact solution of the model by exploiting the replica symmetry. This is the permutation symmetry among the fictitious replicas that are used to perform disorder averages (via the replica trick). In the glassy phase the replica symmetry has to be broken. Using a generalization of the Parisi solution, we provide analytical results for S_n and I_n, and for standard thermodynamic quantities. Both S_n and I_n exhibit a volume law in the whole phase diagram. We characterize the behavior of the corresponding densities S_n/N, I_n/N, in the thermodynamic limit. Interestingly, at the critical point the mutual information does not exhibit any crossing for different system sizes, in contrast with local spin models.

Determination of thermodynamic properties of Ca4Fe9O17 by solid state EMF method

In this study, thermodynamic properties of Ca4Fe9O17 have been measured by electrochemical cells of the type(−)Pt,CaFe2O4+Ca2Fe2O5+Ca4Fe9O17|O2−electrolyte|O2,Pt(+)with an improved experimental apparatus and the sample preparation procedure. The synthesis and heat treatment of the sample electrodes have been developed through a number of trials in order to produce dense and well equilibrated sample electrodes. The phase content of each sample electrode has been separately confirmed by microstructural analysis using secondary electron microscopy (SEM) and measurement of phase compositions using electron probe X-ray microanalysis (EPMA). The interaction between the sample electrode and zirconia electrolyte has been studied in order to optimize measurement procedure, by decreasing unwanted side reactions during the EMF measurements.The standard thermodynamic quantities have been calculated from the measured EMF data involving standard Gibbs energy of formation of Ca4Fe9O17 as well as standard enthalpy. The obtained values have been compared with the thermodynamic functions available in the literature.

Thermodynamic study of the Ag–Sb–Te system with an advanced EMF method

In this work, thermodynamic properties of antimony saturated AgSbTe2 (Ag0.22Sb0.28Te0.50) and silver saturated SbxTe1−x (Ag0.08Sb0.49Te0.43) have been determined by solid state EMF technique with Ag+ ion conducting β″-alumina electrolyte, for the first time. The measurements were done by electrochemical cells of type:(−)Pt, Ag|β″-alumina|Sb2Te3+Ag2Te+SbxTe1−x, Re, Pt(+)Over the temperature range 566⩽T/K⩽620.5 and(−)Pt, Ag|β″-alumina|AgSbTe2+Ag2Te+SbxTe1−x, Re, Pt(+)Over the temperature range 620.5⩽T/K⩽710.The phase transition temperature, where Sb2Te3 and Ag2Te form AgSbTe2 at 101.3kPa pressure, was found to be T=620.5K. Standard thermodynamic quantities of SbxTe1−x and AgSbTe2 were calculated from the results obtained as well as Gibbs energies of formation as linear functions of temperature. Each test electrode, containing 3 phases in equilibrium, was synthetized separately inside an evacuated quartz glass ampoule and quenched into ice water. The contents of the test electrodes were confirmed by SEM–EDS analysis. Also, the average solubility of substances in the test electrodes was calculated from the SEM–EDS data obtained. The parasitic thermovoltage involved with the measured EMF was determined by symmetrical cell arrangement and compensated from the experimental values.

Study of complex formation process between 4′-nitrobenzo-18-crown-6 and yttrium(III) cation in some binary mixed non-aqueous solvents using the conductometry method

The complexation reaction between Y3+ cation and macrocyclic ligand, 4′-nitrobenzo-18-crown-6 (4′NB18C6), was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–1,2-dichloroethane (AN–DCE), acetonitrile–dimethylformamide (AN–DMF) and acetonitrile–ethylacetate (AN–EtOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most cases, the stoichiometry of the complex formed between 4′NB18C6 and Y3+ cation is 1:1 [M:L], but in the case of AN-DCE binary solution (mol% DCE=50) at 15, 25 and 35°C, a 2:1 [M2:L] and also a 2:2 [M2:L2] complexes are formed in solution. The results show that the stoichiometry of the complex formed between 4′NB18C6 and Y3+ cation changes with the composition of the mixed solvents and even with temperature. The stability constant of the 1:1 complex was determined using a computer program, GENPLOT. The stability order of (4′NB18C6.Y)3+ complex in pure studied solvents at 25°C was found to be: EtOAc>AN>MeOH>DMF and in the case of the mixed solvent solutions with 25mol percent of AN at 25°C was: AN-DCE>AN-EtOAc>AN-MeOH∼AN-DMF. The values of stability constant (logKf) of (4′NB18C6.Y)3+ complex which were obtained from conductometric data, show that the stability of the complex is not only affected by the nature and composition of the solvent system, but it is also influenced by the temperature. In all cases, a non-linear behavior is observed for changes of logKf of the (4′NB18C6.Y)3+ complex versus the composition of the binary mixed solvents. The values of standard thermodynamic quantities (ΔH°c and ΔS°c) for the complexation process which were obtained from temperature dependence of the stability constant of (4′NB18C6.Y)3+ complex, show that depending on the solvent system, in most cases, the complex is enthalpy and also entropy stabilized, but in some cases, it is stabilized or destabilized from these view points.