Calculation of the formation enthalpies,standard entropies,and standard heat capacities of alkali and alkaline-earth germanates

The formation enthalpies, standard entropies, and standard heat capacities of alkali and alkaline-earth germanates were determined by regression analysis with allowance for error in the initial data (weights). The potentialities of the presented method of calculation appreciably grew due to the possibility to enhance the array of initial data independently of the crystal structure of compounds. The thermodynamic properties of alkali germanates were estimated for the first time and could be used in the physicochemical models of magmatic melts.     

The thermodynamic properties of alkali metal compounds at high temperatures

A research program has been in progress to obtain reliable thermodynamic data on various binary and ternary alkali metal compounds in the temperature range of 300 to 1500 K. To date, heat capacity measurements have been made on cesium and rubidium chromates, dichromates, zirconates, molybdates, dimolybdates, and halides in the temperature range of 300 to 800K. In addition, measurements are planned or are currently in progress on cesium and rubidium chalcogenides, aluminates, uranates, silicates, and several other lithium, sodium, and potassium compounds. The status of the research program is discussed.     

Concentration dependences of the heat capacity of solutions of alkali metal iodides in N-methylpyrrolidone-water mixed solvent at 298.15 K

Heat capacities of solutions of alkali metal iodides (MeI) in N-methylpyrrolidone (MP)-water mixed solvent were measured over the range of compositions. The influence of the composition of the mixed solvent on the heat capacity of MeI-MP-H₂O ternary systems is discussed. Standard partial molar heat capacities $ \bar C_{p_2 }^o $ \bar C_{p_2 }^o (MeI) in the MP-water mixed solvent at 298.15 K are calculated.     

Heat capacity measurement of organic thermal energy storage materials

The heat capacities of tris(hydroxymethyl)aminomethane (TRIS), 2-amino-2-methyl-1,3-propanediol (AMPL), and neopentylglycol (NPG) are measured from (193.15 to 473.15) K by modulated differential scanning calorimetry (MDSC). The heat capacities of the low temperature layered or chain ordered phases, high temperature orientationally disordered phases, and the liquid phases are reported for these compounds. The low temperature heat capacities (193.15 to 280) K of AMPL are reported for the first time. The heat capacities obtained from our MDSC experiments are in good agreement with adiabatic calorimetry measurements.     

Specific heats of alkali metal halides and universal estimates of the surface tension of their melts based on the thermal properties of critical clusters

A dimensionless parameter is determined that relates the thermophysical and capillary characteristics of alkali metal halides. It is shown that the high-temperature surface tension of alkali metal halides can be determined from the results of the high-temperature measurements of specific heat in the temperature range up to their boiling points.     

Thermal properties of poly(ester‐imide)s with C12H24 and C22H44 groups

The thermal properties of poly(4,4′‐phthaloimidobenzoyl‐n‐methyleneoxycarbonyl) with n =12 and 22, abbreviated as PEIM‐12 and PEIM‐22, respectively, have been studied using differential scanning calorimetry (DSC). The heat capacities of the solid states of both polymers were measured and compared to computed heat capacities from approximate vibrational spectra. The deviations from the vibrations‐only heat capacity were used to identify large‐amplitude, conformational motions. The heat capacities of the liquid states were described as linear functions of temperature. They agreed with the liquid heat capacities generated from the ATHAS addition scheme using group contributions derived from polymers containing the same chemical segments as the PEIM‐ns. Knowing the heat capacities for the solid and liquid, the transition parameters could be separated and enthalpies, entropies, and free enthalpies obtained. With these data, the change of the crystallinity with temperature could be computed. In the early stages of solidification both compounds contain significant entropy contributions from conformational ordering of the flexible spacer and little from the rigid, aromatic segments. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 319–328, 2000     

尿嘧啶和5-溴尿嘧啶的低温热容

采用综合物性测量系统(PPMS)的热容测量模块在1.9-300 K温度区间内对两种药物中间体(尿嘧啶和5-溴尿嘧啶)的低温热容进行了测量与研究. 结果表明, 在测量温区内两种化合物的低温热容随温度的上升而逐步增加, 无任何热异常现象产生; 在相同温度下, 5-溴尿嘧啶的热容数值始终高于尿嘧啶. 利用低温热容理论模型对热容数据进行了拟合, 并计算得到了0-300 K温区的摩尔熵变、焓变等热力学函数. 此外, 通过热容拟合数据计算得到的尿嘧啶和5-溴尿嘧啶在298.15 K的标准摩尔规定熵分别为(132.48±1.32)和(165.39±1.65) J·K^-1·mol^-1.     

The volumetric and thermochemical properties of YCl3(aq), YbCl3(aq), DyCl3(aq), SmCl3(aq), and GdCl3(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa

Relative densities and massic heat capacities have been measured for acidified aqueous solutions of YCl₃(aq), YbCl₃(aq), DyCl₃(aq), SmCl₃(aq), and GdCl₃(aq) at T=(288.15, 298.15, 313.15, and 328.15) K and p=0.1 MPa. These measurements have been used to calculate experimental apparent molar volumes and heat capacities which, when used in conjunction with Young’s rule, were used to calculate the apparent molar properties of the aqueous chloride salt solutions. The latter calculations required the use of volumetric and thermochemical data for aqueous solutions of hydrochloric acid that have been previously reported in the literature. The concentration dependences of the apparent molar properties have been modeled using Pitzer ion interaction equations to yield apparent molar volumes and heat capacities at infinite dilution. The temperature and concentration dependences of the apparent molar volumes and heat capacities of each trivalent salt system were modeled using modified Pitzer ion interaction equations. These equations utilized the revised Helgeson, Kirkham, and Flowers equations of state to model the temperature dependences of apparent molar volumes and heat capacities at infinite dilution. Calculated apparent molar volumes and heat capacities at infinite dilution have been used to calculate single ion properties for the investigated trivalent metal cations. These values have been compared to those previously reported in the literature. The differences between single ion values calculated in this study and those values calculated from thermodynamic data for aqueous perchlorate salts are also discussed.     

Heat capacities and thermodynamic functions of d-ribose and d-mannose

The heat capacities of d-ribose and d-mannose have been studied over the temperature range from 1.9 to 440 K for the first time using a combination of Quantum Design Physical Property Measurement System and a differential scanning calorimeter. The purity, crystal phase and thermal stability of these two compounds have been characterized using HPLC, XRD and TG–DTA techniques, respectively. The heat capacities of d-Mannose have been found to be larger than those of d-ribose due to its larger molecular weight, and the solid–liquid transition due to the sample melting has also been detected in the heat capacity curve. The heat capacities of these two compounds have been fitted to a series of theoretical models and empirical equations in the entire experimental temperature region, and the corresponding thermodynamic functions have been derived based on the curve fitting in the temperature range from 0 to 440 K. Moreover, the phase transition enthalpy and melting temperature of these two compounds have also been determined from the heat flows obtained in DSC measurements.

     

Effect of temperature on ionic volumes and heat capacities in methanol

A flow densimeter and flow heat capacity calorimeter have been employed to measure precision densities and specific heats of selected electrolytes and nonelectrolytes in methanol at 20, 25, and 40°C. Apparent molar volumes and heat capacities have been calculated and the corresponding standard state functions, V ^o and C _p, ^o , evaluated. The data have been used, along with known volumes and heat capacity data at 25°C for numerous alkanes, to generate volumes and heat capacities of model compounds for organic electrolytes. Comparison of the thermodynamic functions for the model compounds with those of the corresponding electrolytes at the respective temperatures has made it possible to assign single ion values and to establish the temperature effects of ionic charges on the volumes and heat capacities of solutes.     

The relationship between coefficients of expansion and heat capacities of simple metals

The authors of this paper, being intrigued by statements in the literature that the coefficients of expansion of metals are proportional to the heat capacities, have put these statements to the test. This paper shows that the experimental ratios of coefficients of expansion and heat capacities at constant pressure are indeed a constant for each metal over wide temperature ranges and the constants are in fair agreement with the values computed from theory.     

Effect of rapid solidification on heat capacities of Al-Sr alloys

Heat capacities of both the ingot-like and melt-spun Al-Sr alloys have been measured through the temperature range 373 to 1060 K using differential scanning calorimetry. The experimental results show that rapid solidification has a slight effect on the temperature dependence of the heat capacities of the Al-Sr alloys. The heat capacities of the melt-spun Al-Sr alloys increase more slowly than those of the ingot-like alloys with increasing temperature from 373 to 900 K. Furthermore, the effect of rapid solidification on the heat capacities becomes more obvious with increasing Sr concentration in the Al-Sr alloys. The data of the heat capacities between 373 and 900 K have been fitted with the least square method and a linear dependence on temperature was assumed for that temperature range. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enthalpy and heat capacity of titanium based alloys

Light metal alloys, as aluminium- and titanium based alloys, are of great interest to aerospace industry but thermodynamic information, mainly heat capacity, is often missing. Then we measured on heating the heat content of seven industrial titanium alloys from room temperature to 600°C with the help of a high-temperature Calvet calorimeter (drop method). Their heat capacities were deduced by derivation of the enthalpy with respect to temperature. The departures from Kopp-Neuman law were calculated.     

氮杂冠醚的研究VIII:N-取代-2,3-苯并-10-氮杂-1,4,7,13-四氧杂-环十五-2-烯的合成及其对碱金属离子的配合作用

2,3-苯并-10-氮杂-1,4,7,13-四氧杂-环十五-2-烯与溴代烃或溴代多甘醇单烷基醚, 在无水碳酸钾存在下, 在乙腈中缩合制得N-取代-2,3-苯并-10-氮杂-1,4,7,13-四氧杂-环十五-2-烯化合物(1-11), 取代基为:n-C4H9, i-C5H11,n-C7H15, CH2CH2OCH3, CH2CH2OCH2CH3, CH2CH2OC4H9, (CH2CH2O)CH3, (CH2H2O)2C2H5, (CH2CH2O)2C4H9, CH2CH=CH2, 和CH2Ph。本文还考查了化合物2-4和6-11在室温下, 在氯仿-水体系中, 对苦味酸碱金属(Li^+、Na^+和K^+)盐的配合作用。     

Thermodynamic properties of alkali halides. V. Temperature and pressure dependence of excess free energies in water

A simple equation has been derived relating the temperature dependence of activity functions with excess enthalpies and excess heat capacities. Using experimentally determined parameters at 298.15°K, it is possible to predict osmotic coefficients and mean activity coefficients of alkali halides in water up to 1 m from 273°K to about 350°K. In general, the predicted functions agree with the measured values within the uncertainty of the activity data. An equation is also given for the pressure dependence of the excess free energies, but it was not possible to check the limitation of this equation due to lack of activity data at various pressures.To whom correspondence should be addressed.     

Combining Neopentyllithium with Potassium tert‐Butoxide: Formation of an Alkane‐Soluble Lochmann–Schlosser Superbase

Mixtures of alkyllithium and heavier alkali‐metal alkoxides are often used to form alkyl compounds of heavier alkali metals, but these mixtures are also known for their high reactivity in deprotonative metalation reactions. These organometallic mixtures are often called LiC–KOR superbases, but despite many efforts their constitution remains unknown. Herein we present mixed alkali‐metal alkyl/alkoxy compounds produced by reaction of neopentyllithium with potassium tert‐butoxide. The key to success was the good solubility and temperature‐stability of neopentyl alkali‐metal compounds, leading to hexane‐soluble mixtures, which allowed handling at ambient temperatures and isolation by crystallization. The compounds in solid state and in solution were identified by X‐ray crystallography and NMR spectroscopy as mixtures of lithium/potassium neopentyl/tert‐butoxy aggregates of varying compositions Li_xK_yNp_z(OtBu)_x+y?z.     

Thermodynamic properties of molecular organic crystals containing nitrogen,oxygen and sulfur. III. Molar heat capacities measured by differential scanning calorimetry

In this paper we report on the heat capacities of 18 organic compounds, which form molecular crystals, in the temperature interval 300–450 K. The measurements are performed using DSC technique.