Showing papers on "Standard molar entropy published in 2010"

Solubility of Gallic Acid, Catechin, and Protocatechuic Acid in Subcritical Water from (298.75 to 415.85) K

Abstract: The solubility of gallic acid hydrate, protocatechuic acid, and (+)-catechin hydrate was measured between 298.75 K and 415.85 K using a dynamic flow apparatus. The aqueous solubility of gallic acid hydrate was found to vary between 12.6 g·L−1 at 298.75 K and 2870 g·L−1 at 415.85 K. The aqueous solubility of protocatechuic acid at the same temperatures varied between 29.4 g·L−1 and 1180 g·L−1, respectively, while that of (+)-catechin hydrate varied between 2.26 g·L−1 and 576 g·L−1, respectively. The aqueous solubility of the phenolic compounds was found to increase exponentially with temperature. The temperature dependence of the aqueous solubility of the phenolic compounds was estimated using empirical correlations based on the data presented in this work. The thermodynamic properties such as standard molar enthalpy, standard molar entropy, and standard molar Gibbs energy of solution were also calculated from the solubility data.

Study of Micellar Behavior of SDS and CTAB in Aqueous Media Containing Furosemide—A Cardiovascular Drug

Abstract: Sound velocity and density measurements of aqueous solutions of the anionic surfactant SDS (sodium dodecyl sulfate) and the cationic surfactant CTAB (cetyltrimethylammonium bromide) with the drug furosemide (0.002 and 0.02 mol⋅dm−3) have been carried out in the temperature range 20–40 °C. From these measurements, the compressibility coefficient (β), apparent molar volume (φ v ) and apparent molar compressibility (φ κ ) have been computed. From electrical conductivity measurements, the critical micelle concentrations (CMCs) of SDS and CTAB has been determined in the above aqueous furosemide solutions. From the CMC values as a function of temperature, various thermodynamic parameters have been evaluated: the standard enthalpy change ( $\Delta H_{\mathrm{m}}^{\mathrm{o}}$ ), standard entropy change ( $\Delta S_{\mathrm{m}}^{\mathrm{o}}$ ), and standard Gibbs energy change ( $\Delta G_{\mathrm{m}}^{\mathrm{o}}$ ) for micellization. This work also included viscosity studies of aqueous solutions of SDS and CTAB with the drug in order to determine the relative viscosity (η r). UV-Vis studies have also been carried for the ternary drug/surfactant/water system having SDS in the concentration range 0.002–0.014 mol⋅dm−3. All of these parameters are discussed in terms of drug–drug, drug–solvent and drug–surfactant interactions resulting from of various electrostatic and hydrophobic interactions.

Fundamental questions about entropy III. A kind of mobile order in liquids : preferential contacts between molecular groups

Abstract: At 25°C, in liquid alcohols and in water an O-H proton follows an oxygen atom of a neighbouring molecule in its peregrinations during a fraction (1-γ) of the time (more than 95% for the lower alcohols). During this time the proton can be found only in a part Vo of the standardized domain of the molecule. Neither Vo not are fixed. The highly preferential contacts create in the liquid a kind of mobile order that does not exist in crystalline substances. As a consequence of the mobile order the standardized possibilities of one molecule A of the liquid are reduced by a factor = γ−γ (1-γ)γ-1 (Vo/ 1-γ. This factor is smaller than one. In the case of water there are two such factors, one for the first and the other for the second proton. The mobile order provokes a change in the molar entropy ΔSA mobile order = R In that is therefore negative. is the volume of the solution divided by the number of A molecules. In the series of the normal alcohols, up to hexanol, the changes of γ can be neglected. Vo and the effects of H-bonding on the vibrations can also be considered as constant. As a consequence in this series one expects an increase of the negative value of the entropy of mobile order according to d(−ΔSA mobile order) = R d ln VA. This is confirmed by the differences between the standard entropies of the alcohols and of their homomorphous hydrocarbons. In the vapour phase where H-bonding is negligible, the differences are positive and practically constant: 13.8 ± 0.7 JK−1 mole−1. For the liquids the differences are negative and increase with the molecular weight.

Equilibrium, kinetic and thermodynamic modeling for the adsorption of heavy metals onto chemically modified hydrotalcite

Abstract: The adsorption of heavy metals (Cu(II), Zn(II) and Cd(II)) from aqueous solutions with tannin-immobilized calcined hydrotalcite (TA-HTC) was studied using batch experiment technique. The surface characterizations of the adsorbent were investigated. Kinetic modeling of removal of metals was done using a pseudo-second-order rate expression. The intraparticle mass transfer diffussion of metals on adsorbent represented the rate-limiting step, with the activation energy of 27.05, 24.22 and 21.96 kJ/mol for Cu(II), Zn(II) and Cd(II), respectively. Experimental results showed that the adsorption of metals was selective to be in the order of Cu(II)>Zn(II)>Cd(II). Equilibrium isotherm data for metal ions were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich and Scatchard equations. The Langmuir adsorption isotherm described the adsorption data very well at all studied temperatures. Thermodynamic parameters such as standard enthalpy (ΔH°), standard entropy (ΔS°), standard free energy (ΔG°), activation energy and isosteric enthalpy and entropy were calculated and the results are discussed in detail.

Density and Surface Tension of Ionic Liquid [C2mim][PF3(CF2CF3)3] and Prediction of Properties [Cnmim][PF3(CF2CF3)3] (n = 1, 3, 4, 5, 6)

Abstract: The density and surface tension of the air- and water-stable hydrophobic ionic liquid (IL) 1-ethyl-3-methylimizazolium tris(pentafluoroethyl) trifluorophosphate (CAS Registry No.: 377739-43-0; [C2mim][PF3(CF2CF3)3]) were measured in the range of T = (283.15 to 338.15) K. The other physicochemical properties of the IL [C2mim][PF3(CF2CF3)3] at 298.15 K were estimated in terms of empirical and semiempirical equations, as well as the interstice model theory. These properties include molecular volume, standard molar entropy, lattice energy, the parachor, molar enthalpy of vaporization, interstice volume, thermal expansion coefficient, interstice fraction, and so forth. Then, the physicochemical properties of the ILs [Cnmim][PF3(CF2CF3)3] (n = 1, 3, 4, 5, 6) family were predicted in terms of the estimated values of molecular volume and the parachor.

Studies on the Effect of Amino Acids/Peptide on Micellization of SDS at Different Temperatures

Abstract: Conductivities of (0.001–0.012) m sodium dodecyl sulfate have been determined in water and in the presence of 0.10 m aqueous glycine/alanine/glycylglycine at 298.15, 303.15, 308.15, and 313.15 K. From the specific conductivity data, the critical micellar concentration, degree of counter ion association, degree of counterion dissociation, free energy of transfer of hydrophobic chain from the medium to interior of the micelle, and surface contribution, standard free energy of micellization, standard enthalpy of micellization, and standard entropy of micellization of sodium dodecyl sulfate have been computed. The thermodynamic parameters of micellization and the effect of additives on these parameters have been used to study the interactions present in the micellar systems.

Amphiphilic drug promethazine hydrochloride-additive systems: evaluation of thermodynamic parameters at cloud point

Abstract: At the cloud point (CP, where phase separation occurs), the thermodynamic properties of aqueous buffer solution of the amphiphilic phenothiazine drug promethazine hydrochloride (PMT) are calculated in the presence of various additives (viz., alcohols, surfactants, and polymers). PMT undergoes clouding phenomena, which depend upon the physicochemical conditions (e.g., concentration, pH, temperature, etc.). As the clouding components release their solvated water, they separate out from the solution. Therefore, the CP of an amphiphile can be considered the limit of its solubility. Herein, we report the thermodynamics of clouding in PMT in the presence of additives. The standard Gibbs energy change of solubilization (ΔsG0) for all of the additives is found to be positive. However, the standard enthalpy change (ΔsH0) and the product of temperature and the standard entropy change (TΔsS0) values are negative as well as positive depending upon the type and nature of the additive. The results are discussed on the ...

Predicting Properties of Amino Acid Ionic Liquid Homologue of 1-Alkyl-3-methylimidazolium Glycine

Abstract: Amino acid ionic liquids (AAILs) [C5mim][Gly] (1-pentyl-3-methylimidazolium glycine) and [C6mim][Gly] (1-hexyl-3-methylimidazolium glycine) were prepared by the neutralization method and characterized by 1H NMR spectroscopy and differential scanning calorimetry (DSC). The values of their density, surface tension, and refractive index were measured in the temperature range of 293.15−343.15 (±0.05) K. Since the AAILs can strongly form hydrogen bonds with water, the small amounts of water are difficult to remove from the AAILs by common methods. In order to eliminate the effect of the impurity water, the standard addition method (SAM) was applied to these measurements. In terms of semiempirical method, physicochemical properties molecular volume Vm, standard molar entropy S0, parachor P, surface tension γ, thermal expansion coefficients α, molar refraction Rm, and refractive index nD of the homologue of [Cnmim][Gly] (n = 2−6) were predicted. In comparison with the values of [C2mim][Gly] in literature, the pr...

Thermodynamics at the cloud point of phenothiazine drug chlorpromazine hydrochloride-additive systems

Abstract: An amphiphilic drug chlorpromazine hydrochloride (CPZ), a phenothiazine with neuroleptic activity, undergoes clouding phenomena, which depend upon the physicochemical conditions (e.g., concentration, pH, temperature, etc.). The clouding components release their solvated water and separate out from the solution. Therefore, the cloud point (CP) of an amphiphile can be considered as the limit of its solubility. Herein, we report the energetics of clouding in CPZ in the presence of additives (viz., alcohols, surfactants, and polymers). The standard Gibbs energy change of solubilization (ΔG 0 s ) for all of the additives is found to be positive. However, the standard enthalpy change (ΔH 0 s ) and the product of the temperature and the standard entropy change (TΔS 0 s ) values are negative as well as positive, depending upon the type and nature of the additive, and the results are discussed on the basis of these factors.

Physicochemical Properties of an Ionic Liquid [C2mim][B(CN)4]

Abstract: The density and surface tension of the ionic liquid (IL) [C2mim][B(CN)4] (1-ethyl-3-methylimidazolium tetracyanoborate) were measured in a temperature range from (283.15 to 338.15) K. In terms of Glasser’s semiempirical relation of ILs, the standard molar entropy and the lattice energy of the homologous series of ILs [Cnmim][B(CN)4] were estimated, respectively. Using Kabo’s method and Rebelo’s method, the molar enthalpy of vaporization of [C2mim][B(CN)4], ΔlgHm0 (298 K), at 298 K, and ΔlgHm0 (Tb), at hypothetical normal boiling point, Tb = 680 K, was estimated, respectively. According to the interstice model, the thermal expansion coefficient of [C2mim][B(CN)4], α = 4.77·10−4 K−1, was estimated and was in good agreement with experimental value.

Density and Surface Tension of Amino Acid Ionic Liquid 1-Alkyl-3-methylimidazolium Glutamate

Abstract: An amino acid ionic liquid (AAIL) [C3mim][Glu] (1-propyl-3-methylimidazolium glutamate) was prepared by the neutralization method and characterized by 1H NMR spectroscopy and DSC trace. Since the AAIL has a strong hydrogen bonding ability, the water content (8.41 ± 0.01)·10−3 mass fraction in the IL is difficult to remove by a common method, so trace water becomes the most problematic impurity. To eliminate the effect of the impurity water, the standard addition method (SAM) was applied to the measurement of densities and surface tensions for [C3mim][Glu] in the temperature range of (318.15 to 343.15 ± 0.05) K and (318.15 to 338.15 ± 0.05) K, respectively. Since per methylene (−CH2−) group in the alkyl chains of the imidazolium-based ionic liquids has almost the same chemical environment, using semiempirical methods we may predict physicochemical properties of 1-alkyl-3-methylimidazolium glutamate [Cnmim][Glu] (n = 1, 2, 3, 4, 5, 6): the molecular volume, Vm, the standard molar entropy, S0, the parachor, ...

Adsorption Equilibrium and Thermodynamic Studies of Copper (II) Ions from Aqueous Solutions by Oil Palm Leaves

Abstract: Oil palm leaf powders (OPLP), an agricultural waste material, were used as new non-conventional and low-cost adsorbents for the removal of copper (II) ions from aqueous solution. Batch studies were performed to evaluate and optimize the effects of various parameters such as contact time, pH of the solution, initial metal ion concentrations and adsorbent dosage. Langmuir, Freundlich and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The experimental data fit well with the Langmuir adsorption isotherm, indicating thereby the mono layer adsorption of the copper (II) ions. The monolayer sorption capacity of OPLP for copper (II) ions was found to be 11.22 mg/g at 30 ◦C. The thermodynamic parameters like standard free energy, standard enthalpy, and standard entropy changes for the adsorption of copper (II) ions have also been computed and discussed. The heat of adsorption [∆H◦ = -39.84 kJ/mol] implied that the adsorption was exothermic in nature.

Density, Viscosity, Vapor−Liquid Equilibrium, and Excess Molar Enthalpy of [Chloroform + Methyl tert-Butyl Ether]

Abstract: Density and viscosity measurements in the T = (273.15 to 318.15) K range of pure chloroform and methyl tert-butyl ether (MTBE), as well as of the binary system [x1 chloroform + (1 − x1) MTBE] over the whole concentration range at T = 293.15 K, were made. The experimental results for the pure components were fitted to empirical equations, which permit the calculation of these properties in the studied temperature range. Calculated values are in agreement with the experimental ones. Data of the binary mixture were further used to calculate the excess molar volume and viscosity deviations. The excess molar enthalpy at T = (303 ± 1) K and vapor−liquid equilibrium measurements at T = (303.15 ± 0.05) K were also measured for the binary system. These last experimental results were used to calculate activity coefficients, the excess molar Gibbs energy, and excess molar entropy. This binary system shows strong negative deviations from ideality and exhibits a minimum pressure azeotrope, whose coordinates are: P = (...

Experimental and Computational Studies on the Structural and Thermodynamic Properties of Two Sulfur Heterocyclic Keto Compounds

Abstract: The present work reports the standard (p° = 0.1 MPa) molar enthalpies of formation in the gaseous phase of thioxanthone, (91.9 ± 2.4) kJ·mol−1, and tetrahydrothio-γ-pyrone, (−164.6 ± 2.0) kJ·mol−1, at T = 298.15 K, derived from their standard molar energies of combustion and standard molar enthalpies of sublimation, measured by rotating-bomb combustion calorimetry and by the vacuum drop microcalorimetric technique, respectively. For comparison purposes, we performed additional standard ab initio molecular orbital calculations, using the G3(MP2)//B3LYP composite procedure, which were used for the calculation of the enthalpies of several homodesmotic reactions, allowing us to extract the standard molar enthalpies of formation, in the gaseous phase, of the two heterocycles considered in this work. The calculated results are in excellent agreement with the experimental data. The three-dimensional structure of the crystal tetrahydrothio-γ-pyrone was also determined by X-ray crystallography.

Prediction of Thermochemical Properties for Gaseous Ammonia Oxide

Abstract: Ammonia oxide (NH3O), a zwitterionic tautomer of hydroxylamine (NH2OH), has been identified to explain the high reactivity of NH2OH. Recent evidence has shown that ammonia oxide exists in the condense phase and aqueous solution. However, neither experimental nor theoretical data of its thermochemical properties are presently available. In this work, thermochemical parameters of ammonia oxide are calculated, under standard conditions, using isodesmic reactions at several theoretical methods (HF, MP2, B3LYP, G2, G2MP2, G3, G3B3, and CBS-Q) and several basis sets (Dunning correlation-consistent and Pople-style). To monitor the computed values, the values of hydrogen peroxide are calculated by the same methods and compared with the experimental data. The quantum chemistry calculations predict the value of molar enthalpy of formation to be (55.7 ± 2.9) kJ·mol−1 and molar Gibbs energy of formation to be (103.8 ± 2.9) kJ·mol−1, for gaseous ammonia oxide at 1 atm and 298.15 K. The determined molar entropy and mol...

Effect of temperature on ion exchange equilibrium between AMX membrane and binary systems of Cl−, NO− 3 and SO2− 4 ions

Abstract: The effect of the temperature variation on ion exchange equilibrium between an anion exchange membrane and solutions of electrolytes containing the most dominant anions of natural waters (CI−, NO− 3 and SO2minus; 4) was studied. All experiments were carried out at 0.3 mol l−1. AMX membrane experimented in this work is a commercial product provided by TOKUYAMA SODA. Humidity percentage and ion exchange capacity were determined. Ionic exchange isotherms for the binary systems (CI−/NO−)3,(CI−/SO2− 4) and (NO− 3 / SO2− 4) were established at different temperatures from 283 to 313 K. At 283 and 298 K, the affinity order was: CI− > NO− 3 > SO2− 4. This order was NO− 3 > CI− > SO2− 4 at 313 K. Selectivity coefficients Kj i and thermodynamic equilibrium constants K0j i calculated for uni-univalent and uni-bivalent ions exchange reaction system increase with increasing temperature. Thermodynamic parameters such as standard free enthalpy change, standard enthalpy change, and standard entropy change were calculated....

Crystal Structure, Phase Transition, and Thermodynamic Properties of Bis‐dodecylammonium Tetrachlorozincate (C12H25NH3)2ZnCl4(s)

Abstract: The crystal structure and composition of (C12H25NH3)(2)ZnCl4(s) were characterized by chemical and elemental analysis. X-ray powder diffraction technique and X-ray crystallography. The lattice energy of the title compound was calculated to be U-POT=888.82 kJ.mol(-1). Low temperature heat capacities of the title compound have been measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 403 K. An obvious solid to solid phase transition occurred in the heat capacity curve, and the peak temperature, molar enthalpy and molar entropy of the phase transition of the compound were determined to be T-trs=(364.02 +/- 0.03) K, Delta H-trs(m) = (77.567 +/- 0.341) kJ.mol(-1), and Delta S-trs(m)=(213.77 +/- 1.17) J.K-1.mol(-1), respectively. Experimental molar heat capacities before and after the phase transition were respectively fitted to two polynomial equations. The smoothed molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were calculated and tabulated at an interval of 5 K.

Low-temperature heat capacity and standard entropy of PdO(cr.)

Abstract: The temperature dependence of the heat capacity C o = f(T) of palladium oxide PdO(cr.) was studied for the first time in an adiabatic vacuum calorimeter in the range of 6.48–328.86 K. Standard thermodynamic functions C o (T), H o(T) — H o(0), S o(T), and G o(T) — H o(0) in the range of T → 0 to 330 K (key quantities in different thermodynamic calculations with the participation of palladium compounds) were calculated on the basis of the experimental data. Based on an analysis of studies on determining the thermodynamic properties of PdO(cr.), the following values of absolute entropy, standard enthalpy, and Gibbs function of the formation of palladium oxide are recommended: S o(298.15) = 39.58 ± 0.15 J/(K mol), Δf H o(298.15) = −112.69 ± 0.32 kJ/mol, Δf G o(298.15) = −82.68 ± 0.35 kJ/mol. The stability of Pd(OH)2 (amorph.) with respect to PdO(cr.) was estimated.

Energetics and molecular structure of 2,5-dimethyl-1-phenylpyrrole and 2,5-dimethyl-1-(4-nitrophenyl)pyrrole.

Abstract: Thermochemical and thermodynamic properties of 2,5-dimethyl-1-phenylpyrrole and 2,5-dimethyl-1-(4-nitrophenyl)pyrrole have been determined by using a combination of calorimetric and effusion techniques as well as high-level ab initio molecular orbital calculations. The standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline state, ΔfHm° (cr), at T = 298.15 K, were derived from the standard molar enthalpies of combustion, ΔcHm°, which were obtained from static bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to determine the standard molar enthalpies of sublimation, ΔcrgHm°, at T = 298.15 K. From the experimental results, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, were derived. The results were analyzed and interpreted in terms of enthalpic increments and molecular structure. For comparison purposes, standard ab initio molecular calculations at the G3(MP2)//B3LYP level were performed, using a set of working reactions an...

Heat Capacity, Enthalpy of Formation, and Entropy of Methyl Carbamate

Abstract: The heat capacity (Cp) of methyl carbamate (MC) was measured with an adiabatic calorimeter. The standard enthalpy of formation (ΔfH0(cr, 298.15 K)) and the standard entropy (S0(cr, 298.15 K)) for MC were determined. Thus, Cp(T) values of MC were obtained for the crystal and liquid forms in the temperature range of 298.15−433.10 K. A quadratic trinomial was used to correlate the data of Cp(T). The enthalpy of fusion of MC was measured using differential scanning calorimetry (DSC), and its sublimation enthalpy was estimated. The gas-phase standard enthalpy of formation (ΔfH0(g, 298.15 K)) of MC was calculated via the method of group contribution developed by Benson. Based on the above data, the values of ΔfH0(cr, 298.15 K) and S0(cr, 298.15 K) of MC were estimated to be −513.57 kJ/mol and 77.1 J mol−1 K−1, respectively. A thermochemical cycle including a reversible reaction was designed to examine the reliability of the estimated values by measuring the equilibrium constant of the reaction. The results show...