Standard Molar Volumes and Heat Capacities of Aqueous Solutions of Trifluoromethanesulfonic Acid at Temperatures up to 573 K and Pressures to 30 MPa

Densities and heat capacities of dilute aqueous solutions (0.025 to 0.4 mol⋅kg⁻¹) of trifluoromethanesulfonic acid (triflic acid) were measured with original high-temperature, high-pressure instruments at temperatures and pressures up to 574 K and 31 MPa, respectively. Standard molar volumes and standard molar heat capacities were obtained via extrapolation of the apparent molar properties to infinite dilution. The evolution of these standard derivative properties of triflic acid with temperature and pressure is qualitatively compared with that of other acids of different strengths.     

Apparent molar volumes and heat capacities of aqueous solutions of sodium benzenesulfonate at 25°C

Apparent molar volumes and heat capacities of sodium benzenesulfonate have been measured at 25°C and at molalities up to 1.1 molal using a Picker flow densimeter and a Picker flow heat capacity calorimeter. Data for both properties have been modeled with Pitzer equations for the respective functions, and the standard state values evaluated. The apparent molar volume of sodium benzenesulfonate appears to be relatively insensitive to sample preparation. Possible reasons for the difference in the apparent molar volume reported here and the literature value are discussed.     

Excess molar heat capacities of (<Emphasis Type="Italic">L</Emphasis>-glutamine aqueous solution+<Emphasis Type="Italic">D</Emphasis>-glutamine aqueous solution) at temperatures between 293.15 and 303.15 K

Summary Excess molar heat capacities of (L-glutamine aqueous solution+D-glutamine aqueous solution) were determined by using a differential scanning calorimeter at temperatures between 293.15 and 303.15 K. Excess molar heat capacities are all negative. Excess molar heat capacities decrease with increasing temperature.     

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.     

吡啶-2,6-二甲酸氢钾的合成、结构表征及热化学性质

合成了吡啶-2,6-二甲酸氢钾(KHDPC). 利用X射线单晶衍射仪确定了化合物的晶体结构. 用精密自动绝热热量计测量了其在78~360 K温度区间的低温热容. 利用最小二乘法对配合物的实验热容进行拟合, 得到热容随温度变化的多项式方程. 利用此方程计算出温度区间内的舒平热容值及相对于298.15 K时的热力学函数值. 利用Hess定律设计合理的热化学循环, 在等温环境下利用溶解-反应热量计分别测定所设计热化学反应的反应物和产物在所选溶剂中的溶解焓并计算出反应的反应焓. 最后, 计算出该化合物的标准摩尔生成焓为-(1052.69±1.52) kJ/mol.     

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.     

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.     

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.     

The partial molar heat capacities of glycine and glycylglycine in aqueous solution at elevated temperatures and atp = 10.0 MPa

Apparent molar heat capacities have been determined for aqueous solutions of glycine at temperatures from 352.09 K to 470.63 K and glycylglycine at temperatures from 352.09 K to 423.15 K. Both systems were investigated at a pressure of 10.0 MPa. Measurements were performed with a differential flow calorimeter that is capable of operation at temperatures  > 723 K and pressures to approximately 40.0 MPa. Partial molar heat capacities at infinite dilution have been calculated from apparent molar values and have been corrected for “relaxation" contributions. The reported partial molar heat capacity values for aqueous glycine and glycylglycine solutions have been modelled using the revised Helgeson, Kirkham, and Flowers semi-empirical equations of state. These models for solutions of glycine and glycylglycine in water have been compared with those previously reported in the literature.     

Molar heat capacities for (1-butanol + 1,4-butanediol, 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol) as function of temperature

The isobaric molar heat capacities for the binary mixtures (1-butanol + 1,4-butanediol) were determined in the temperature range from (293 to 353) K from measurements of isobaric specific heat capacity in a differential scanning calorimeter. The composition dependencies of the excess molar isobaric heat capacities obtained from the experimental results were fitted by the Redlich-Kister polynomials. Above T = 303.15 K, the excess isobaric molar heat capacities are negative over the whole composition range and absolute values increase with temperature. For temperatures (293.15 and 298.15) K, the excess values show S-shaped character. These excesses are however in general very small; at the temperature 298.15 K smaller than 0.1 J · K⁻¹ · mol⁻¹.Additionally, the isobaric molar heat capacities of 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol were determined over a similar temperature range. The experimental data for all diols are compared with available literature data and values estimated from group additivity.     

烟酸钠Na(C6H4NO2)(s)的低温热容和热化学

选择分析纯烟酸和无水醋酸钠作为反应物, 用室温固相合成方法合成了无水烟酸钠. 利用FTIR和X射线粉末衍射等方法进行了表征, 利用化学分析和元素分析确定其组成为Na(C6H4NO2). 用精密自动绝热热量计测量其在78~400 K温度区间的低温热容. 研究结果表明, 该化合物在此温度区间无热异常现象发生. 用最小二乘法将实验摩尔热容对温度进行拟合, 得到热容随温度变化的多项式方程. 用此方程进行数值积分, 得到在此温度区间每隔5 K的舒平热容值和相对于298.15 K时的热力学函数值. 在此基础上, 通过设计合理的热化学循环, 选用1 mol/L NaOH溶液作为量热溶剂, 利用等温环境溶解-反应热量计分别测得固相反应的反应物和产物在所选溶剂中的溶解焓, 得到固相反应的反应焓. 最后, 计算出无水烟酸钠的标准摩尔生成焓为: ΔfHm0[Na(C6H4NO2), s]=-(548.96±1.11) kJ/mol.     

Thermodynamic properties of the binary mixture of water and <Emphasis Type="Italic">n</Emphasis>-butanol

The molar heat capacities of the binary mixture composed of water and n-butanol were measured with an adiabatic calorimeter in the temperature range 78–320 K. The functions of the heat capacity with respect to thermodynamic temperature were established. A glass transition, solid–solid phase transition and solid–liquid phase transition were observed. The corresponding enthalpy and entropy of the solid–liquid phase transition were calculated, respectively. The thermodynamic functions relative to a temperature of 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature.     

吡啶-2,6-二甲酸氢锂的合成、结构及热化学性质

以甲醇和水的混合溶液为溶剂, 合成了吡啶-2,6-二甲酸氢锂Li(HDPC)(H₂O)(s), 利用X射线单晶衍射法表征了其晶体结构. 用精密自动绝热热量计测量了其在78～378 K温区的低温热容. 通过最小二乘法拟合得到摩尔热容随折合温度变化的多项式方程, 利用此方程计算出了化合物的舒平热容和各种热力学函数. 设计合理的热化学循环, 利用等温环境溶解-反应热量计分别测定所设计热化学反应的反应物和产物在选定溶剂中的溶解焓, 通过计算得到反应焓为-(46.83 ±0.16) kJ/mol. 利用Hess定律计算出吡啶-2,6-二甲酸氢锂的标准摩尔生成焓为-(747.90 ±1.46) kJ/mol. 利用紫外-可见光谱仪对反应物和产物溶液的测量证实所设计热化学循环的可靠性.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

烟酸的低温热容和标准摩尔生成焓

利用精密自动绝热热量计测量了分析纯烟酸在78～400 K温区的低温热容. 用最小二乘法将实验摩尔热容对温度进行拟合, 得到了热容随温度变化的多项式方程. 用此方程进行数值积分, 得到在此温区每隔5 K的舒平热容值和相对于298.15 K时的热力学函数值. 利用精密静止氧弹燃烧热量计测定了烟酸在298.15 K时的恒体积燃烧能为 Δ_cU＝ －(24528.3±16.1) J•g^－1. 依据物质燃烧焓定义计算出烟酸的标准摩尔燃烧焓为: Δ_cH_m^o＝－(3019.05±1.98) kJ•mol^－1. 最后, 依据Hess定律计算出烟酸的标准摩尔生成焓为: Δ_fH_m^o＝－(56.76±2.13) kJ•mol^－1.     

Thermodynamics of Aqueous Diethylenetriaminepentaacetic Acid (DTPA) Systems: Apparent and Partial Molar Heat Capacities and Volumes of Aqueous H2DTPA3−, DTPA5−, CuDTPA3−, and Cu2DTPA− from 10 to 55°C

Apparent molar heat capacities and volumes have been determined for aqueous solutions of the mixed electrolytes Na₅DTPA + NaOH, Na₃CuDTPA + NaOH, and NaCu₂DTPA + NaOH, and the single electrolyte Na₃H₂DTPA (DTPA=diethylenetriaminepentaacetic acid) at temperatures from 10 to 55°C. The experimental results have been analyzed in terms of Young's rule with the Guggenheim form of the extended Debye–Hückel equation and the Pitzer ion-interaction model. These calculations led to standard partial molar heat capacities and volumes for the species H₂DTPA^3–(aq), DTPA^5–(aq), CuDTPA^3–(aq), and Cu₂DTPA^–(aq) at each temperature. The partial molar properties at 0.1 m ionic strength were also calculated. The standard partial molar properties were extrapolated to elevated temperatures with the revised Helgeson–Kirkham–Flowers (HKF) model. Values for the partial molar heat capacities from the HKF model have been combined with the literature data to estimate the ionization constants of H₂DTPA^3–(aq) and the formation constant of the CuDTPA^3–(aq) copper complex at temperatures up to 300°C.     

无水苯甲酸锂的合成、结构表征及热化学研究

用分析纯苯甲酸和一水氢氧化锂作为反应物, 采用水热合成法制得苯甲酸锂. 利用X射线粉末衍射、FTIR、元素分析及化学分析等方法对样品进行组成和结构表征. 采用精密自动绝热热量计测量了其在80~400 K范围内的摩尔热容, 利用最小二乘法将此温区热容实验值对折合温度进行拟合, 得到热容随温度变化的多项式方程. 通过设计合理的热化学循环, 选用0.1 mol/L HCl溶液作为量热溶剂, 利用等温环境溶解-反应热量计分别测定合成反应的反应物和产物在所选溶剂中的溶解焓, 得到反应焓Δ_rH_m⁰=-(9.75±0.27) kJ/mol. 利用Hess定律计算出苯甲酸锂的标准摩尔生成焓Δ_fH_m⁰(C₆H₅COOLi, s)=-(307.82±0.57) kJ/mol.     

Heat capacities of a series of terminal linear alkyldiamides determined by DSC

Molar heat capacities of twelve linear alkane-α,ω-diamides H₂NOC-(CH₂)_(n-2)-CONH₂, (n=2 to 12 and n=14) were measured by differential scanning calorimetry at T=183 to 323 K. Heat flow rate calibration of the Mettler DSC 30 calorimeter was carried out by using benzoic acid as reference material. The calibration was checked by determining the molar heat capacity of urea in the same temperature range as that of measurements. The molar heat capacities of alkane-α,ω-diamides increased in function of temperature and fitted into linear equations. Smoothed values of C _p,m at 298.15 K displayed a linear increase with the number of carbon atoms. The C _p,m contribution of CH₂ group was (22.6±0.4) J K⁻¹ mol⁻¹, in agreement with our previous results concerning linear alkane-a,ω-diols and primary alkylamides as well as the literature data on various series of linear alkyl compounds. On leave from the Faculty of Chemistry, University of Craiova, Calea Bucureşti 165, Craiova 1100, Romania     

Low‐Temperature Heat Capacities and Standard Molar Enthalpy of Formation of Gramine (C11H14N2)

Low‐temperature heat capacities of gramine (C₁₁H₁₄N₂) were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 401 K. A polynomial equation of heat capacities as a function of temperature was fitted by least squares method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at 5 K intervals. The constant‐volume energy of combustion of the compound at T=298.15 K was measured by a precision oxygen‐bomb combustion calorimeter as Δ_cU=−(35336.7±13.9) J·g⁻¹. The standard molar enthalpy of combustion of the compound was determined to be Δ_cH_m⁰=−(6163.2±2.4) kJ·mol⁻¹, according to the definition of combustion enthalpy. Finally, the standard molar enthalpy of formation of the compound was calculated to be Δ;_cH_m⁰=−(166.2±2.8) kJ·mol⁻¹ in accordance with Hess law.     

Heat capacities and thermodynamic properties of 2-benzoylpyridine (C12H9NO)

The heat capacities of 2-benzoylpyridine were measured with an automated adiabatic calorimeter over the temperature range from 80 to 340 K. The melting point, molar enthalpy, Δ_fusH^m, and entropy, Δ_fusS^m, of fusion of this compound were determined to be 316.49±0.04 K, 20.91±0.03 kJ mol^–1 and 66.07±0.05 J mol^–1 K^–1, respectively. The purity of the compound was calculated to be 99.60 mol% by using the fractional melting technique. The thermodynamic functions (H_T–H_298.15) and (S_T–S_298.15) were calculated based on the heat capacity measurements in the temperature range of 80–340 K with an interval of 5 K. The thermal properties of the compound were further investigated by differential scanning calorimetry (DSC). From the DSC curve, the temperature corresponding to the maximum evaporation rate, the molar enthalpy and entropy of evaporation were determined to be 556.3±0.1 K, 51.3±0.2 kJ mol^–1 and 92.2±0.4 J K^–1 mol^–1, respectively, under the experimental conditions.