Heats of solution of gaseous hydrocarbons in water at 25°C

The heats of solution at 25°C for a number of hydrocarbon gases are reported as measured by a calorimetric method. There is excellent agreement between the standard enthalpy changes of solution measured calorimetrically and those derived from high precision temperature dependent solubility measurements. However the calorimetrically determined standard enthalpies of solution of a number of gases are greatly improved over values obtained from low precision temperature dependent solubility measurements. A method is presented to readily estimate the standard errors in the standard enthalpy change for any process derived from the temperature dependence of the equilibrium constant for the process. Comparison of the standard enthalpies and entropies of solution of hydrocarbon gases in water shows that the standard free energies of solution for all hydrocarbon gases investigated are dominated by unfavorable entropy contributions. A strong linear correlation between the standard entropy of solution and the number of hydrogens in the hydrocarbon molecule is found. This correlation suggests that the hydrocarbon hydrophobic effect is regulated by the number of allowable configurations of a water molecule in contact with each C–H group.     

时间分辨脉冲光声量热法及其应用

光声量热法是一种研究快速光化学反应的新方法，已广泛应用于有机和有机金属化学中涉及自由基中间体以及生物体系中光诱导化学反应生成亚稳态物质的动力学和热力学性质的研究。本文介绍了光声量热的基本原理、实验装置和它在化学、生物体系中的应用。     

Dynamik linearer Molekülanionen in den Hydrogensulfiden von Natrium,Kalium und Rubidium: Differential-Scanning-Kalorimetrie,Röntgen- und Neutronenbeugung

Dynamical Behaviour of Linear Molecular Anions in the Hydrogensulfides of Sodium, Potassium and Rubidium: Differential Scanning Calorimetry, X-ray and Neutron Diffraction Hydrogensulfides of the alkali metals M ? Na, K, Rb were prepared in autoclaves by the reaction of the corresponding metals with H₂S and D₂S, respectively, in the temperature range from 50°C to 150°C. Differential scanning calorimetry, X-ray and neutron diffraction methods reveal that both, the HS^?-and DS^?-compounds occur in three crystalline modifications with HT ? high-, MT ? medium- and LT ? low-temperature form: The temperatures and enthalpies for the changes of modifications of the H- and D-compounds are given and the atomic arrangements revealed mainly by neutron diffraction data are discussed, in relation to, for example, size of cations.     

稀土高氯酸盐-谷氨酸配合物[Pr2(L-α-Glu)2(ClO4)(H2O)7](ClO4)3•4H2O的低温热容和热化学研究

合成了一种稀土高氯酸盐-谷氨酸配合物. 经TG/DTG、化学和元素分析、FTIR及与相关文献对比, 确定其组成为[Pr₂(L-α-Glu)₂(ClO₄)(H₂O)₇](ClO₄)₃•4H₂O, 纯度为99.0%以上. 利用显微熔点仪分析发现其没有熔点. 在78～370 K温区, 用精密绝热量热仪测量其低温热容, 在285～306 K温区发现一明显吸热峰, 归结为固-固相变过程. 通过相变温区三次重复热容测量, 得到相变温度T_tr、相变焓Δ_trH_m和相变熵Δ_trS_m分别为(297.158±0.280) K, (12.338±0.016) kJ•mol^－1和(41.520±0.156) J•K^－1•mol^－1. 用最小二乘法将非相变温区的热容对温度进行拟合, 得到了热容随温度变化的两个多项式方程. 用此方程进行数值积分, 得到每隔5 K的舒平热容值和相对于273.15 K的热力学函数值. 根据TG/DTG结果, 推测了该配合物的热分解机理. 依据Hess定律, 选择1 mol•dm^－3盐酸为量热溶剂, 利用等温环境溶解-反应量热计, 测定了该配合物的标准摩尔生成焓为: Δ_fH_m⁰＝－(7223.1±2.4) kJ•mol^－1.     

Total luminescence intensity (TLI) offers superior early oxidation detection in unstabilised polyethylene but is no better than FT-IR for stabilised polyolefins

In an earlier study, we have shown that chemiluminescence (CL) and the total luminescence intensity (TLI) method are highly sensitive to oxidation in degradable PE. In this study, stabilised PE and PP were characterised with CL in an inert (TLI) and in an oxygen atmosphere (CL-OIT) and the results were compared to those obtained by the commonly used techniques, FT-IR (carbonyl index (CI)) and thermal analysis (DSC-OIT). PE was aged at a low temperature (80 °C) and PP was aged at temperatures between 60 and 120 °C. Non-Arrhenius behaviour was observed in the oxidation of PP. This showed the importance of aging at a low temperature to obtain realistic results. TLI and CI of stabilised PP and most of the stabilised PE gave comparable results with the same sensitivity for oxidation detection. This was in contrast to our previous results for degradable PE. However, TLI of unstabilised PE showed earlier oxidation detection than CI, which agreed with our earlier results. TLI of PE had a higher sensitivity than CL-OIT, and both TLI and CI of PP were sufficiently sensitive to detect the effect of aging at different temperatures, whereas DSC-OIT was not.     

Silver(I) Complexes with Nitrogen-Containing Noncyclic, Macrocyclic, and Macrobicyclic Ligands in Propylene Carbonate

Stability constants and thermodynamic data for complex formation of silver(I) with noncyclic, macrocyclic, and macrobicyclic ligands have been measured in propylene carbonate using potentiometric and calorimetric methods. All ligands containing two nitrogen donor atoms form extremely stable complexes. Only if substituents reduce the basicity of the nitrogen donor atoms, the stability of the complexes decreases drastically. However, the cryptand (221) forms the most stable complex of all ligands examined. In this case, the dimensions of the ligand cavity and of the cation are nearly identical.     

Effect of the complex forming ion on the physicochemical characteristics of solvation of tetraphenylporphine complexes

The enthalpies of dissolution, transfer, and axial coordination for the Cd(II), Co(II), Mn(III), Fe(III), and Cr(III) complexes of tetraphenylporphine, H₂(TPP), in nonpolar (C₆H₆, CCl₄) and electron-donating solvents (DMF, DMSO, Py,c-C₅H₁₀NH) have been determined calorimetrically at 298.15 K. On the basis of thermogravimetrical data for the corresponding crystallosolvates the composition, thermal stability, and energy of intermolecular interaction of the metal-porphine complexes with pyridine have been calculated. Complexing in noncoordinating solvents brings about no radical change in the physicochemical characteristics of axial coordination which depend critically on the electron structure of the complex-forming metal.Translated fromfzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 846–850, May, 1993.     

Calorimetric investigation of the adsorption of binary vapour mixtures of tetrahydropyrrol with methanol and cyclopentane on the homogeneous surface

Adsorption isotherms and differential heats of adsorption of tetrahydropyrrol (THP) and cyclopentane CP), as well as THP and methanol mixtures (mole ratio 1∶1, 1∶2 and 1∶4) on the graphitized carbon black Sterling MT surface were determined. The influence of dilution of [THP] on its ability to undergo homomolecular association was tested. Even 1∶4 dilution of THP does not prevent is association. Methanol strongly interacts with THP in the mixed adsorbed layer forming heteromolecular associates.     

Enthalpies of formation of methoxybenzoic acids and their dependence on structure

The energy of combustion of 2,5-dimethoxybenzoic acid has been determined using a static bomb calorimeter. The vapor pressures of the compound have been measured over a 18 K temperature interval by the Knudsen effusion technique. Heat capacity measurements betweenT=270 K andT=338 K were carried out by DSC. From these experimental results the standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous state at the temperature 298.15 K have been derived. With this compound, the series of mono- and dimethoxy-benzoic acids have been completed. Their_f H _m ^o values were expressed by an additive relationship, taking into account the number of methoxy groups and the number of all 1,2 interactions: an accuracy of 3.3 kJ·mol^–1 was achieved. In an alternative approach the substituent effect of the methoxy groups was evaluated within the framework of isodesmic reactions. The effect of disubstitution was referred to mono derivatives and the excess energy—the so-called buttressing effect—was evaluated (2–24 kJ· mol^–1 for individual bis derivatives). These values were explained in terms of the conformation of the methoxy group around the C_ar-O bond.     

微孔和介孔材料中的热化学

这篇论文综述了美国加州大学戴维斯分校科学院院士Navrotsky课题组多年来在多孔材料上取得的一系列热化学研究结果。讨论了热化学对微孔、介孔材料的结构稳定性和合成过程的影响。借助多种测热手段对影响骨架结构的热焓、热熵和自由能进行了系统的测量和计算。研究数据表明一系列纯硅分子筛、介孔材料和磷酸铝多孔材料同相应的石英相和块磷铝矿相相比能量上最多只高出15 kJ·mol-1。一系列纯硅分子筛的熵值比石英相高出3.2—4.2 J·K-1·mol-1；在0—12.6 J·K-1·mol-1范围内相对应的自由能几乎没有差别。因此，对不同微孔、介孔材料，其骨架结构在能量上是几乎没有区别的。另外，本文通过介绍一种新型测热方法——原位测热，揭示了分子筛合成过程中的动力学和成核/结晶机理。