Thermodynamics of complex formation equilibria between Ag(I) and thiocarbonyl ligands in propan-2-one (acetone) solution

Complex formation equilibria in propan-2-one between Ag(I) and thiourea (Tu), thioacetamide (Ta), N-methylthiourea (MeTu), N-ethylthiourea (EtTu), N,N′-diethylthiourea (Et₂Tu), N-phenylthiourea (PhTu), N, N′-diphenylthiourea (Ph₂Tu), and thiobenzanilide (TbAn) have been investigated by potentiometry at different temperatures t = 0–20 °C and self-determined ionic medium. Formation of mono-, bis-, and tris-coordinated AgL _n complexes (charges are omitted) has been detected, but for Ag(I)–Ph₂Tu system, where the occurrence of the mono-coordinate AgPh₂Tu and bis-coordinate Ag(Ph₂Tu)₂ has been found. The stability constants have been deduced. The standard enthalpy and entropy changes have been evaluated from the linear dependence of the free energies on temperature.     

Thermodynamic Properties of Aqueous Solutions of Lithium Chloride

Vapor pressure of aqueous solutions of lithium chloride were measured by differential static method, in a concentration range of 12.9-44.2% weight and in the temperature range of 30-100°C. The experimental data were fitted to the Antoine type equation: log P = A( m ) + B( m )/ T + C( m )/ T 2 , where A, B, and C are constants which are concentration dependent. Enthalpies of solution were calculated by the Haltenberger method using experimental vapor pressure data and heat capacity data. The Duhring and enthalpy-concentration charts have been constructed. These charts may be useful in the performance studies of absorption heat pumps.     

Effect of alumina on enthalpy of mixing of mixed alkali silicate glasses

The enthalpy of mixing of mixed alkali (Na₂O and K₂O) silicate glasses containing various concentrations of alumina was determined using an ion-exchange equilibrium method. For glasses with a constant alkali concentration, the enthalpy of mixing was found to become less negative with alumina addition. Consistent with our previous results on the enthalpy of mixing of alumina-free mixed alkali silicate glasses, the magnitude of enthalpy of mixing exhibited a good correlation with the molar volume mismatch of the corresponding two single alkali glasses as well as with the extent of conductivity mixed alkali effect, e.g. excess activation energy of conductivity, ΔE. The reduction of the magnitude of the enthalpy of mixing with alumina addition can be attributed to the reduction of non-bridging oxygen and ionic field strength. Combining the present results with results obtained earlier, the magnitude of the enthalpy of mixing for all mixed alkali (Na₂O and K₂O) silicate glasses with and without alumina was expressed by a simple function of a modified Tobolsky parameter, which takes into account the alkali concentration and the difference in cation-to-effective anion distances. The enthalpy of mixing data of the mixed alkali glasses was then compared with reported experimental data on the conductivity of mixed alkali aluminosilicate glasses. What appears to be conflicting experimental data can be understood in terms of the magnitude of the enthalpy of mixing and we can conclude that the mixed alkali effect is closely correlated with the negative enthalpy of mixing.     

An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

The vaporization enthalpies and liquid vapor pressures from T = 298.15 K to T = 400 K of 1,3,5-triazine, pyrazine, pyrimidine, and pyridazine using pyridines and pyrazines as standards have been measured by correlation-gas chromatography. The vaporization enthalpies of 1,3,5-triazine (38.8 ± 1.9 kJ mol⁻¹) and pyrazine (40.5 ± 1.7 kJ mol⁻¹) obtained by these correlations are in good agreement with current literature values. The value obtained for pyrimidine (41.0 ± 1.9 kJ mol⁻¹) can be compared with a literature value of 50.0 kJ mol⁻¹. Combined with the condensed phase enthalpy of formation in the literature, this results in a gas-phase enthalpy of formation, Δ_f H _m (g, 298.15 K), of 187.6 ± 2.2 kJ mol⁻¹ for pyrimidine, compared to a value of 195.1 ± 2.1 calculated for pyrazine. Vapor pressures also obtained by correlation are used to predict boiling temperatures (BT). Good agreement with experimental BT (±4.2 K) including results for pyrimidine is observed for most compounds with the exception of the pyridazines. The results suggest that compounds containing one or two nitrogen atoms in the ring are suitable standards for correlating various heterocyclic compounds provided the nitrogen atoms are isolated from each other by carbon. Pyridazines do not appear to be evaluated correctly using pyridines and pyrazines as standards.     

Numerical analysis of the thermal behaviour of a shell-and-tube heat storage unit using phase change materials

This work presents a numerical study of a latent heat storage unit (LHSU) consisting of a shell-and-tube. The shell space is filled with two phase change materials (PCMs), P116 and n-octadecane, with different melting temperatures (50 °C and 27.7 °C, respectively). A heat transfer fluid (HTF: water) flows by forced convection through the inner tube, and transfers the heat to PCMs. In order to compare the thermal performances of the latent heat storage unit using two phase change materials (LHSU2) and a single PCM (LHSU1), a mathematical model based on the conservation energy equations was developed and validated with experimental data. Several numerical investigations were conducted in order to examine the impact of the key parameters: the HTF inlet temperature (ranges from 50 to 60 °C), the mass flow rate of the HTF and the proportion mass of PCMs, on the thermal performances of the latent heat storage units using two PCMs and a single PCM, during charging process (melting). This parametric study provides guidelines for system thermal performance and design optimization.     

Thermodynamic properties of Fe-Ni solid solutions studied by Fe Mössbauer spectroscopy

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for Ni_1−xFe_x solid solutions with x in the range 0.01≤x≤0.10. The obtained data were analysed in terms of short range order parameter (SRO) and the binding energy E_b between two iron atoms in the studied materials using the extended Hrynkiewicz-Królas idea. It was found that the binding energy is positive or Fe atoms interact repulsively. The extrapolated value of E_b for x=0 was used for computation of enthalpy of solution of Fe in Ni. Finally the values of enthalpies of solution were used to predict the mixing enthalpy curve for the Fe-Ni solid solutions. The results were compared with corresponding value given in the literature, which was calculated theoretically using DFT techniques, as well as with the value obtained from experimental calorimetric data and resulting from the cellular atomic model of alloys by Miedema.     

用相互作用势指数估算单取代烷烃生成焓

基于直链烷烃生成焓的实验值提出16种取代基X(OH、SH、NH₂、Br、Cl、I、NO₂、CN、CHO、COOH、CH₃、CH=CH₂、C≡CH、Ph、COCH₃、COOCH₃)的相互作用势指数IPI(X). 用IPI(X)和极化效应指数建立模型,对单取代烷烃RX(包括含支链的化合物)的生成焓进行估算,所得回归方程有良好的相关性,该模型既考虑了基团R和X的贡献,又考虑了R与X相互作用的贡献. 并采用留一法对其稳定性和预测能力进行验证.