Apparent Molar Heat Capacities and Apparent Molar Volumes of Aqueous 1,1,1,3,3,3-Hexafluoroisopropanol at Different Temperatures

Specific heats and apparent molar heat capacities of aqueous 1,1,1,3,3,3-hexafluoroiso- proanol (HFIP) have been determined at temperatures from 20.0 to 45.0°C using micro differential scanning calorimetry in the molality range of 0.06741 to 1.24053 mol-kg^{– 1}. Densities and apparent molar volumes have also been determined for aqueous HFIP at temperatures from 10.3 to 30.0°C using digital densimetry in the molality range of 0.04009 to 0.67427 mol-kg^{– 1}. The results of these measurements have been used to calculate the following partial molar quantities and temperature derivatives for aqueous HFIP as a function of temperature: C_p,2,m°, (C_p,2,m°/T)_p, (²C_p,2,m°/T²)_p, V_2,m° and (V_2,m°/T)_p. The contribution of the — F atom to the partial molar heat capacity and volume has been calculated. The results have been explained in terms of structural changes in water in aqueous HFIP solution. The results obtained in this work contain essential information needed for the development of an equation of state for this system, when used in combination with other thermodynamic properties of aqueous HFIP.     

Apparent Molar Volumes and Heat Capacities of Nucleating Lysozyme Solutions at 25°C

Densities and heat capacities of lysozyme in Na-acetate buffer (pH 4.2) containing 0.64 m sodium chloride at 25°C were determined by Anton Paar 60/602 digital densimeter and differential scanning adiabatic calorimeter DASM-4 in the range of lysozyme concentration 0.000499–0.002450 m. The measurements were made after 1, 24 and 48 h of the dissolution of lysozyme in the buffer. The changes of the values of apparent molar volumes and heat capacities in time were observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Densities and Apparent Molar Volumes of Aqueous NaNO3 Solutions at Temperatures from 292 to 573 K and at Pressures Up to 30 MPa

Densities of four aqueous NaNO₃ solutions (0.100, 0.303, 0.580, 0.892 mol-kg^–1 H₂O) have been measured in the liquid phase with a constant-volume piezometer immersed in a precision liquid thermostat. Measurements were made at ten isotherms between 292 and 573 K. The range of pressure was 0.1–30 MPa. The total uncertainty of density, pressure, temperature, and concentration measurements were estimated to be less than 0.06%, 0.05%, 10 mK, and 0.014%, respectively. Values of saturated densities were determined by extrapolating experimental P- data to the vapor pressure at fixed temperature and composition. Apparent molar volumes were derived using measured values of density for the solutions and for pure water. The apparent molar volumes were extrapolated to zero concentration to yield partial molar volumes at infinite dilution. The temperature, pressure, and concentration dependence of partial and apparent molar volumes were studied. The measured values of density and apparent and partial molar volume were compared with data reported in the literature.     

Thermodynamic Properties of Aqueous Dimethylamine and Dimethylammonium Chloride at Temperatures from 283 K to 523 K: Apparent Molar Volumes, Heat Capacities, and Temperature Dependence of Ionization

Data for the apparent molar volumes of aqueous dimethylamine and dimethylammonium chloride have been determined with platinum vibrating tube densimeters at temperatures 283.15 K T 523.15 K and at different pressures. Apparent molar heat capacities were measured with a Picker flow microcalorimeter over the temperature range 283.15 K T 343.15 K at 1 bar. At high temperatures and steam saturation pressures, the standard partial molar volumes of dimethylamine and dimethylammonium chloride deviate towards positive and negative discontinuities at the critical temperature and pressure, as is typical for many neutral and ionic species. The revised Helgeson-Kirkham-Flowers (HKF) model and fitting equations based on the appropriate derivatives of solvent density have been used to represent the temperature and pressure dependence of the standard partial molar properties. The standard partial molar heat capacities of dimethylamine ionization , calculated from both models, are consistent with literature data obtained by calorimetric measurements at T 398 K to within experimental error. At temperatures below 523 K, the standard partial molar volumes of dimethylamine ionization agree with those of morpholine to within 12 cm³-mol^-1, suggesting that the ionization of secondary amine groups in each molecule is very similar. The extrapolated value for of dimethylamine above 523 K is very different from the values measured for morpholine at higher temperature. The difference is undoubtedly due to the lower critical temperature and pressure of (CH₃)₂NH(aq).     

Measurements of the Molar Heat Capacities and Excess Molar Heat Capacities for Acetonitrile + Diethylamine or sec-Butylamine Mixtures at Various Temperatures and Atmospheric Pressure

As a continuation of our studies of the excess functions of binary systems containing acetonitrile (1−x)–amines (x) mixtures, the molar heat capacity, Cp, and excess molar heat capacity, Cp ^E, of acetonitrile + diethylamine or sec-butylamine mixtures have been determined as a function of composition at 288.15, 293.15, 298.15 and 303.15 K at atmospheric pressure using a modified 1455 PARR solution calorimeter. The excess heat capacity data are positive for both systems over the whole composition range. The experimental data on the excess molar heat capacity are discussed in terms of the influence of the magnitude of the experimental excess molar enthalpy, H ^E, over the curve shaped for the experimental Cp ^E data, molecular interactions in the mixtures, isomeric effect of the amines and modeling of Cp ^E data.     

气体摩尔热容的拓展性教学

物质的摩尔热容是热量传递、熵增、焓变等计算中的重要参数之一。为让学生全面掌握摩尔热容的概念及其计算方法,以气体为例,基于文献调研,对理想气体、范德瓦尔斯气体、昂尼斯气体、雷德利克-邝气体的摩尔热容进行了系统化地归纳分析。利用热力学第一定律及热力学相关公式导出了改进型雷德利克-邝气体的摩尔热容。并对气体摩尔热容与物态方程的内在联系、摩尔定压热容与摩尔定体热容的差别进行了讨论与分析。这些研究结果对气体摩尔热容的拓展性教学及学生的创新性自学具有较好的参考价值。     

氨基酸-醇-水体系的密度与表观摩尔体积

用DMA602/60型震动管数字密度计测定了298.15 K下甘氨酸、丙氨酸分别在纯水和四个不同浓度甲醇、乙醇和丙醇水溶液中的密度, 计算了相应的表观摩尔体积, 用最小二乘法拟合了氨基酸在醇水溶液中的标准偏摩尔体积. 根据McMillan-Mayer理论拟合了水溶液中氨基酸分别与醇相互作用的对相互作用参数Vab和三相互作用参数Vabb, Vaab. 结果表明甘氨酸、丙氨酸在醇水溶液中的表观摩尔体积都随醇浓度的增加而增加, 都属亲水破坏性溶质; 其自相互作用参数和三相互作用参数均为正值, 对相互作用参数Vab均为负值且随烃基链的延长, 负值依次增大. 分别根据极性分子的相互作用模型、结构水化模型和溶剂分离缔合模型进行了讨论.     

Molar Volumes and Heat Capacities of Electrolytes and Ions in Nonaqueous Solvents: 1. Formamide

Apparent molar volumes and heat capacities of 27 electrolytes have been measured as a function of concentration in formamide at 25°C using a series-connected flow densimeter and Picker calorimeter system. These data were extrapolated to infinite dilution using the appropriate Debye–Hückel limiting slopes to give the corresponding standard partial molar quantities. Ionic volumes and heat capacities at infinite dilution were obtained by an appropriate assumption based on the reference electrolyte Ph₄PBPh₄ (TPTB). The ionic volumes, but not the heat capacities, agree reasonably well with previously published statistically based predictions. The values obtained are discussed in terms of simple models of electrolyte solution behavior and a number of interesting features are noted, including, possible dependencies of ionic volumes on solvent isothermal compressibility and of ionic heat capacities on solvent electron acceptor abilities.     

Apparent Molar Volumes and Adiabatic Compressibilities of Crown Ethers and Glymes in Aqueous Solutions at Various Temperatures

Apparent molar volumes and adiabatic compressibilities of 18-crown-6,15-crown-5, 12-crown-4, tetraglyme, and triglyme were measured at 15, 25, and40°C. Apparent molar expansibilities andK ^o Tvalues were also determined.The contribution of the -CH₂CH₂O- group to the limiting partial molar volumesand compressibilities of cyclic and open-chain ethers are compared. It isconcluded, on the basis of the compressibility results, that there is a subtle differencebetween the hydration of the ethene-oxide group in cyclic and open-chain ethers.     

Thermodynamics of Aqueous Nitrilotriacetic Acid (NTA) Systems: Apparent and Partial Molar Heat Capacities and Volumes of Aqueous HNTA2−, NTA3−, MgNTA−, CoNTA−, NiNTA− and CuNTA− at 25 °C

Apparent molar heat capacities and volumes have been determined for aqueous Na₂HNTA, Na₃NTA, NaMgNTA, NaCoNTA, NaNiNTA and NaCuNTA at 25 °C. The experimental results have been analyzed in terms of Young’s rule with an extended Debye–Hückel equation to obtain standard partial molar heat capacities C _p ^o and volumes V ^o for the species HNTA²⁻(aq), NTA³⁻(aq), MgNTA⁻(aq), CoNTA⁻(aq), NiNTA⁻(aq) and CuNTA⁻(aq), at ionic strengths I = 0 and I = 0.1 mol⋅kg⁻¹. Values of C _p ^o and V ^o were combined with the literature data to estimate the stability constants of the NTA complexes at temperatures up to 100 °C.     

Application of the Bjerrum Association Model to Electrolyte Solutions. IV. Apparent Molar Heat Capacities and Compressibilities in Water and Aprotic Solvents

The Bjerrum association model, which has already been applied successfully to volumes and enthalpies of dilution of electrolyte solutions, has now been extended to apparent molar heat capacities and compressibilities of these systems. The proposed method of calculation, which takes into account the relaxation effect observed in second derivatives of the excess Gibbs free energy, can be used to extrapolate to infinite dilution the experimental data for systems showing a wide range of association constants in acetonitrile, propylene carbonate, and water. The concentration dependence of the thermodynamic properties can be reproduced quantitatively by the addition of one or two virial coefficients. Literature data for C _P,2, and K _S,2, of electrolytes in aprotic solvents were refitted with this equation. For dissociated or slightly associated systems (K _A < 10), the standarY ₂ ^o d infinite dilution quantities () are in excellent agreement with literature values. For systems with high K _A, Y ₂ ^o obtained by the model are systematically lower than those reported in the literature. This is not surprising, since the traditional method of extrapolation using the Debye–Hückel limiting law or the Pitzer equation does not take association into account. A computer software that performs the calculations for the application of the Bjerrum model to thermodynamic properties has been designed and is presented in the appendix.     

The Partial Molar Volume and Heat Capacity of the Glycyl Group in Aqueous Solution at 25^C

The partial molar volumes, V₂ ^{^}, and the partial molar heat capacities, C_p,2 ^{^}, at infinite dilution have been determined for three new peptides of sequence seryl(glycyl)_xglycine, where x=0 to 2, in aqueous solution at 25^{^}C. Values for V₂ ^{^} at 25^°C have also been determined for two neutral peptide derivatives N-acetylglycylglycinamide and N-acetylglycylglycylglycinamide. These V₂ ^°; and C_p,2 ^°; results were used to estimate the partial molar volume and heat capacity of the backbone glycyl group, CH₂CONH, of proteins in aqueous solution at 25^°;C. The results obtained are compared with those calculated using partial molar data for alternative model compounds. The new glycyl group contributions are in excellent agreement with those currently used in our group additivity schemes for the calculation of the partial molar volumes and heat capacities of unfolded proteins.     

Heat Capacities of Aqueous Solutions of Acetone; 2,5-Hexanedione; Diethyl Ether; 1,2-Dimethoxyethane; Benzyl Alcohol; and Cyclohexanol at Temperatures to 523 K

The heat capacities of aqueous solutions of acetone, 2,5-hexanedione, diethyl ether, 1,2-dimethoxyethane, benzyl alcohol and cyclohexanol at concentrations of 0.1 to 1.0 mol⋅kg⁻¹ were determined at temperatures of 298.15, 423.15, 473.15 and 523.15 K and pressures up to 28 MPa. The measurements were performed at ambient conditions using the commercial Picker differential flow calorimeter and at high temperatures and pressures with a customized Picker type calorimeter constructed at the Blaise Pascal University, Clermont-Ferrand. Standard molar heat capacities were obtained by weighted extrapolation to the infinite dilution limit. The contributions of –CO–, –O– and –OH groups to the standard molar volume and standard molar heat capacity were determined from the newly determined and literature data. The variation of the three oxygen-containing group contributions with temperature and molecular structure is examined qualitatively.     

Apparent Molar Volumes of Symetric and Asymetric Tetraalkylammonium Salts in Dilute Aqueous Solutions

The apparent molar volumes, V_φ of tetramethylammonium, tetraethylammonium, tetrabutylammonium, butyltriethylammonium, dibutyldiethylammonium, and tributylethylammonium bromides have been measured at 298.15K in the concentration range from 0.01 to 0.04mol⋅kg⁻¹. The concentration dependence of V_φ is given using the Redlich and Meyer relation. The apparent molar volume at infinite dilution, V∘_φ, and the empirical constant, B_V, have been calculated. The CH₂-group contribution has been obtained by the additivity rule. The results were interpreted in terms of solute–solvent interactions.     

不同温度下水溶液中树胶醛糖与HCl相互作用的体积性质

采用密度法研究了在278.15—318.15 K(间隔10 K)下树胶醛糖+HCl+水三元溶液的密度、树胶醛糖在盐酸(0.2—2.1087 mol/kg)中的表观摩尔体积VΦ,A、标准表观摩尔体积VΦ,A0和树胶醛糖与HCl的体积相互作用参数. 研究结果表明, 树胶醛糖在盐酸中的VΦ,A和VΦ,A0均随HCl浓度的增加而线性增大. 在一定温度下, 树胶醛糖从纯水到盐酸水溶液的标准转移表观摩尔体积均为正值, 且随盐酸浓度的增加而增大. 在所测温度范围内, 树胶醛糖在盐酸中的VΦ,A0随温度T的变化关系可表示为VΦ,A0=b0+b1(T-273.15)0.84. 树胶醛糖与HCl对体积相互作用参数VEN大于零, 但数值很小且对温度变化不甚敏感.     

Densities and Apparent Molar Volumes of Aqueous H<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript>BO<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript> Solutions at Temperatures from 296 to 573 K and at Pressures up to 48 MPa

Densities of four aqueous H₃BO₃ solutions (0.062, 0.155, 0.315, and 0.529 mol-kg^–1) have been measured in the liquid phase with a constant volume piezometer immersed in a precisely controlled liquid thermostat. Measurements were made at temperatures between 296 and 573 K and pressures from 0.82 to 48 MPa. The total uncertainties of the density, pressure, temperature, and molality measurements were estimated to be less than 0.06%, 0.05%, 10 mK, and 0.0005 mol-kg^–1, respectively. The accuracy of the method was confirmed by PVT measurements on pure water for two isobars (30 and 39 MPa) at temperatures from 313 to 573 K. The experimental and calculated (IAPWS formulation) densities for pure water show excellent agreement which is within their experimental uncertainties (average absolute deviation, AAD=0.012%;). Apparent and partial molar volumes were derived using the measured densities for solutions and pure water, and these results were extrapolated to zero concentration to yield the partial molar volumes of the electrolyte (H₃BO₃) at infinite dilution. The temperature, pressure, and concentration dependencies of the apparent and partial molar volumes were studied. Small pressure and concentration effects on the apparent molar volumes were found at temperatures up to 500 K. The parameters of a polynomial type of equation of state for the specific volume V_sol(P, T, m) as a function of pressure, temperature, and molality were obtained with a least-squares method using the experimental data. The root-mean-square deviation between measured and calculated values from this polynomial equation of state is ±0.2 kg-m^–3 for density. Measured values of the solution densities and the apparent and partial molar volumes are compared with data reported in the literature.     

Interactions of Phenylalanine,Tyrosine and Histidine in Aqueous Caffeine Solutions at Different Temperatures

Densities, ρ, viscosities, η, and refractive indices, n_D of aqueous caffeine (0.5 M) and of solutions of amino acids, l‐phenylalanine (Phe), l‐tyrosine (Tyr) and l‐histidine (His), (0.01–0.05 M) in aqueous‐caffeine have been measured at 298.15, 303.15, 308.15 and 313.15 K. From these experimental data, apparent molar volume, ?_v, limiting partial molar volume, ?^º_ν and the slope, S_v, transfer volume, ?^º_ν,tr, Falkenhagen coefficient, A, Jones‐Dole coefficients, B, free energies of activation per mole of solvent, Δμ^o#₁ and per mole of solute, Δμ^o#₂, enthalpy, ΔH^* and entropy, ΔS^* of activation of viscous flow, and molar refraction, R_m were calculated. The results are interpreted from the point of view of solute‐solvent and solute‐solute interactions in these systems. It has been observed that there exist strong solute‐solvent and weak solute‐solute interactions in these systems. Further, the solute‐solvent interactions decrease, whereas solute‐solute interactions increase with rise in temperature. It is observed that these amino acids act as structure‐makers in aqueous‐caffeine solvent. The thermodynamics of viscous flow have also been discussed.     

Excess Molar Volumes of Aqueous Solutions of Butylamine Isomers

Abstract

Excess molar volumes (V^E ) and average thermal expansivities (α) of the systems, water (W) + n-butylamine (NBA), W + sec-butylamine (SBA), and W + tert-butylamine (TBA), have been calculated from the density data at temperatures ranging from 298.15–323.15 K. The V^E and α values have been plotted as functions of mole fraction of amines. The systems show large negative excess volumes, magnitude of which varies in the order, W + TBA > W + SBA > W + NBA. The curves are found to be symmetrical along the composition axis, with minima occurring at 0.5 mole fraction of butylamines. The negative excess volumes have been interpreted primarily by two effects: (i) strong chemical interaction leading to the formation of 1:1 complexes through H-bonding and (ii) hydrophobic hydration causing significant contraction of volume.     

Apparent Molar Volumes of Benzyltrimethylammonium Bromide and Its Homologs in Aqueous Solution at 15, 25, and 35°C

Apparent molar volumes at infinite dilution of benzyltrimethylammonium bromide and its butyl and hexyl homologs at 15, 25, and 35°C and of dibenzyldimethylammonium bromide at 25°C in aqueous solution were estimated from density measurements. The additivity rule for the contribution of the methylene groups to the apparent molar volumes was found to be obeyed within a broad range of homologs, which covers the parent salt and the dodecyldimethylbenzylammonium bromide. The volumetric contribution of the phenylene (–C₆H₄–) group was estimated to be 61 cm³-mol^–1 at 25°C. A value of –16.9 ± 0.3 cm³-mol^–1 was suggested for the volumetric contribution of the N⁺ fragment to the apparent molar volume of alkylbenzyldimethylammonium salts.     

Densities,Apparent Molar Volumes and Viscosities of Concentrated Aqueous NaNO<Subscript>3</Subscript> Solutions at Temperatures from 298 to 607 K and at Pressures up to 30 MPa

Densities of four (2.124, 2.953, 5.015 and 6.271 mol-kg⁻¹) and viscosities of eight (0.265, 0.503, 0.665, 1.412, 2.106, 2.977, 5.015 and 6.271 mol-kg⁻¹) NaNO₃(aq) solutions have been measured with a constant-volume piezometer immersed in a precision liquid thermostat and using capillary flow techniques, respectively. Measurements were made at pressures up to 30 MPa. The temperature range was 298–607 K for the density measurements and 298–576 K for the viscosity measurements. The total uncertainty of density, viscosity, pressure, temperature and composition measurements were estimated to be less than 0.06%, 1.6%, 0.05%, 15 mK and 0.02%, respectively. The temperature, pressure and concentration dependence of density and viscosity of NaNO₃(aq) solutions were studied. The measured values of density and viscosity of NaNO₃(aq) were compared with data and correlations reported in the literature. Apparent molar volumes were derived using the measured density values. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for strong electrolytes. The values of the viscosity A-, B-, D- and F-coefficients of the extended Jones–Dole equation for the relative viscosity (η/η₀) of NaNO₃(aq) solutions were evaluated as a function of temperature. The derived values of the viscosity A- and B-coefficients were compared with the results predicted by Falkenhagen–Dole theory of electrolyte solutions and calculated with the ionic B-coefficient data.