Bestimmung der Bildungsenthalpie von SmOCl durch Lösungskalorimetrie

Determination of the Enthalpy of Formation of SmOCl by Solution Calorimetry The enthalpy of formation of SmOCl (ΔH(SmOCl_f, 298) = —239.9 ± 0.5 kcal/mol) was determined from the heat of solution of SmOCl (ΔH_L(SmOCl_f298) = —31.24 ± 0.15 kcal/mol) on the base of the enthalpies of formation of Sm₂O₃ and SmCl₃ and their heats of solution in 4n HCl.     

Thermochemistry of heteroatomic compounds

The enthalpies of combustion (H _comb) of 13 primary, secondary, and tertiary alkylphoshines in the condensed state were calculated using the equation H _comb = –860.7 – 107.0N, where N is the number of valent (bond-forming) electrons. This equation can be used for the calculation of enthalpies of combustion and formation of phosphoric acid esters.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1693–1694, August, 2004.     

Reduction-reoxidation behavior of manganese cation-deficient spinels

Thermogravimetry and electrical conductivity were used to study the reduction-reoxidation behavior of submicronic manganese-cation-deficient spinels. The aim is to control the hydrogen reduction of a number of Fe³⁺ ions in partially oxidized spinels at room temperature so that an “original state” can be obtained. In more oxidized spinels at 400°C, the availability for reduction of Fe³⁺ ions is much less than that of Mn³⁺ ions in octahedral sites. The reduced phase could be reoxidized to the original oxygen level and further oxidation-reduction cycles resulted in no change in cation distribution but were accompanied by sintering.     

Thermochemistry of heteroatomic compounds

The enthalpies of solvation of four geometric isomers of 2,5-dimethyl-1-phenyl-1-thioxophosphorinan-4-one in chloroform, nitrobenzene, and methanol were calculated using the enthalpies of vaporization of the isomers determined by the modified Solomonov—Konovalov method from the enthalpies of solution of the compounds in CCl₄ andp-xylene and molar refractions. The enthalpies of formation (ΔH _f ^o) of the isomers in the condensed and gas phase were assessed in the framework of Benson's group additivity scheme by summing the ΔH _f ^o values for phosphacycloketone fragments obtained from molecular mechanics calculations with the contributions of the phenyl group and S atom attached to the P atom. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1533–1536, September, 2000.     

A calorimetric and thermodynamic investigation of A2[(UO2)2(MoO4)O2] compounds with A = K and Rb and calculated phase relations in the system (K2MoO4 + UO3 + H2O)

A calorimetric and thermodynamic investigation of two alkali-metal uranyl molybdates with general composition A₂[(UO₂)₂(MoO₄)O₂], where A = K and Rb, was performed. Both phases were synthesized by solid-state sintering of a mixture of potassium or rubidium nitrate, molybdenum (VI) oxide and gamma-uranium (VI) oxide at high temperatures. The synthetic products were characterised by X-ray powder diffraction and X-ray fluorescence methods. The enthalpy of formation of K₂[(UO₂)₂(MoO₄)O₂] was determined using HF-solution calorimetry giving Δ_fH° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = −(4018 ± 8) kJ · mol⁻¹. The low-temperature heat capacity, С_р°, was measured using adiabatic calorimetry from T = (7 to 335) K for K₂[(UO₂)₂(MoO₄)O₂] and from T = (7 to 326) K for Rb₂[(UO₂)₂(MoO₄)O₂]. Using these С_р° values, the third law entropy at T = 298.15 K, S°, is calculated as (374 ± 1) J · K⁻¹ · mol⁻¹ for K₂[(UO₂)₂(MoO₄)O₂] and (390 ± 1) J · K⁻¹ · mol⁻¹ for Rb₂[(UO₂)₂(MoO₄)O₂]. These new experimental results, together with literature data, are used to calculate the Gibbs energy of formation, Δ_fG°, for both phases giving: Δ_fG° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = (−3747 ± 8) kJ · mol⁻¹ and Δ_fG° (T = 298 K, Rb₂[(UO₂)₂(MoO₄)], cr) = −3736 ± 5 kJ · mol⁻¹. Smoothed С_р°(Т) values between 0 K and 320 K are presented, along with values for S° and the functions [H°(T) − H°(0)] and [G°(T) − H°(0)], for both phases. The stability behaviour of various solid phases and solution complexes in the (K₂MoO₄ + UO₃ + H₂O) system with and without CO₂ at T = 298 K was investigated by thermodynamic model calculations using the Gibbs energy minimisation approach.     

Thermochemistry of the mixed calcium phosphate Ca8P2O7(PO4)4

The calcium mixed phosphate Ca₈P₂O₇(PO₄)₄ has been synthesized by thermal decomposition of octacalcium phosphate previously prepared by precipitation in ammoniacal phosphate solution. The enthalpy of formation at 298.15 K referenced to β-tricalcium phosphate and calcium pyrophosphate is determined. β-Tricalcium phosphate was prepared by two methods: precipitation in ammoniacal aqueous medium and high temperature solid-state reaction. Calcium pyrophosphate was prepared by high temperature solid-state reaction. All the compounds are characterized by chemical analysis, X-rays diffraction and IR spectroscopy. The enthalpy of formation +10.83 ± 0.63 kJ mol⁻¹ is obtained by solution calorimetry at 298.15 K in nitric acid.     

Calorimetric study on oxidation of alumina supported rhodium by dioxygen

Rhodium particles in nanometer size were prepared by impregnating alumina powders with aqueous solutions containing rhodium salts. The dispersion (D) of rhodium crystallites on the prepared samples was estimated by dioxygen adsorption measured at 300 K. Phenomena of oxidizing the supported crystallites with 2.5 × 10⁴ Pa O₂ in a temperature range between 280 and 870 K were calorimetrically studied. Extent of oxidation may be distinguished into three stages, i.e., adsorption on surface (T < 300 K), progressive penetration into bulk, and formation of a stable bulk oxide (T> 700 K), on raising the oxidation temperature. Heat of dioxygen adsorption varies only slightly with the dispersion (D) of rhodium and has a value of 294 ± 6 kJ (mol O₂)⁻¹. Chemical stoichiometry of the bulk oxide formed, however, varies with the dispersion of rhodium crystallites. A dioxide (RhO₂) (_f H = 225 ± 3 kJ (mol O₂)⁻¹) and a sesquioxide (Rh₂O₃) (_f H = 273 ± 3 kJ (mol O₂)⁻¹) was formed at D < 60% and D> 80%,     

Thermochemistry of uracil and thymine revisited

Thermochemical properties of uracil and thymine have been evaluated using additional experiments. Standard (p⁰ = 0.1 MPa) molar enthalpies of formation in the gas phase at T = 298.15 K for uracil −(298.1 ± 0.6) and for thymine −(337.6 ± 0.9) kJ · mol⁻¹ have been derived from energies of combustion measured by static bomb combustion calorimetry and molar enthalpies of sublimation determined using the transpiration method. The G3 and G4 quantum-chemical methods were used for calculations of theoretical gaseous enthalpies of formation being in very good agreement with the re-measured experimental values.     

On-line calorimetry as a technique for process monitoring and control in biotechnology

This contribution reviews laboratory-scale investigations carried out on the usefulness of biological heat release measurements, as a means for monitoring and controlling the metabolic state of microbial cultures. Such studies are carried out in high-quality bench-scale calorimeters, but measuring heat generation rates by establishing energy balances ought to be applicable to large-scale bioreactors without resorting to sophisticated instrumentation. The signal received can either be interpreted by more qualitative correlation with the evolution of the culture, or it may be quantitatively exploited - together with other on-line measurements - in order to assess the rates at which various types of metabolisms proceed in the culture. The work described shows how this can be used to keep a culture in a desired metabolic state during fed-batch and transient continuous cultures of the yeast, S. cerevisae, and how a bacterial fed-batch culture can be controlled in order to optimize biosynthesis of an antibiotic.     

Thermochemistry of copper complex of 6-benzylaminopurine

The copper(II) complex of 6-benzylaminopurine (6-BAP) has been prepared with dihydrated cupric chloride and 6-benzylaminopurine. Infrared spectrum and thermal stabilities of the solid complex have been discussed. The constant-volume combustion energy, Δ_c U, has been determined as −12566.92±6.44 kJ mol⁻¹ by a precise rotating-bomb calorimeter at 298.15 K. From the results and other auxiliary quantities, the standard molar enthalpy of combustion, Δ_c H _m ^θ, and the standard molar of formation of the complex, Δ_f H _m ^θ, were calculated as −12558.24±6.44 and −842.50±6.47 kJ mol⁻¹, respectively.     

Standard enthalpies of formation of selected XYZ half-Heusler compounds

The standard enthalpies of formation of selected ternary half-Heusler type compositions XYZ (X = Au, Co, Fe, Ir, Ni, Pd, Pt, Rh, Ru; Y = Hf, Mn, Ti, Zr; Z = Ga, Sn) were measured using high temperature direct reaction calorimetry. The measured standard enthalpies of formation (in kJ/mole of atoms) of the half-Heusler compounds (prototype MgAgAs, Pearson symbol cF12, space group F-43m) are, IrMnSn (−29.4 ± 1.8); NiTiSn (−52.6 ± 2.4); PtHfSn (−98.8 ± 3.4); PtMnSn (−55.8 ± 2.6); PtTiSn (−93.6 ± 3.3); PtZrSn (−104.9 ± 3.8); for the B2 compound (prototype CsCl, Pearson symbol cP2, space group Pm-3m), RuMnGa (−26.9 ± 1.7); for the C1 structured (prototype CaF₂, Pearson symbol cF12, space group Pm-3m) or the C1_b structured compound IrMnGa (−40.9 ± 1.7). Indicative standard enthalpies of formation of the following compounds were obtained, half-Heusler compounds AuMnSn, CoTiSn, IrZrSn, NiHfSn, NiZrSn, PdHfSn, PdZrSn, RhTiSn; Heusler compound (prototype Cu₂MnAl, Pearson symbol cF16, space group Fm-3m) RhMnSn; hexagonal compound (prototype BeZrSi, Pearson symbol hP6, space group P6₃/mmc) PtMnGa and another type of hexagonal compound (prototype RhHfSn, Pearson symbol hP18, space group P-62c) RhHfSn, IrZrsn, RhZrSn. Values were compared with ab initio calculations from AFLOW and OQMD. Lattice parameters of these compounds were determined using X-ray diffraction (XRD) analysis. Microstructures were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Selected alloys were further annealed to investigate phase transformations and phase relationships.     

水合偏硼酸钾的热化学研究

Hydrated potassium monoborate(KBO₂·4/3H₂O) was obtained from an aqueous solution in a mole ratio of K₂O∶B₂O₃=2∶1 and characterized by powder X-ray diffraction(XRD)， infrared spectroscopy(FT-IR) and Raman spectroscopy. The enthalpy of solution of hydrated potassium monoborate， KBO₂·4/3H₂O， in approximately 1mol·dm^-3 aqueous hydrochloric acid was determined. Together with the previously determined enthalpies of so-lution of H₃BO₃ in approximately 1mol·dm^-3 HCl(aq) ，and of KCl in aqueous(hydrochloric acid+boric acid)， the standard molar enthalpy of formation of -(1411.11±0.84)kJ·mol^-1 for KBO₂·4/3H₂O was obtained from the standard molar enthalpies of formation of KCl(s)， H₃BO₃(s)， and H₂O(l). The standard molar entropy of formation of -422.94J·K^-1·mol^-1 and standard molar entropy of 163.47J·K^-1·mol^-1 for KBO₂·4/3H₂O were calculated from the thermodynamic relations. A group contribution method is applicable to KBO₂·4/3H₂O.     

Thermochemistry of molecular complexes. 4. Molecular complexes of I2 with chloromethylbenzenes

The enthalpy of formation for twelve molecular complexes of I₂ with chloromethylbenzene molecules in CCl₄ have been determined. The wavelength of maximum absorption for each complex is also reported. The formation enthalpy for the complexes appears to depend strongly on the number and type of substituent groups attached to the benzene ring, but only weakly on the location of the substituent group on the ring. This suggests that it should be possible to predict formation enthalpies for a wide variety of complexes of this type based on a limited number of experimental measurements.     

Thermochemistry of aromatic ketones. Experimental enthalpies of formation and structural effects

The standard enthalpies of formation Δ_fH^o (liq. or cr.) at the temperature T = 298.15 K were measured using combustion calorimetry for benzophenone (A), 1-indanone (B), -tetralone (C), 9-fluorenone (D), anthrone (E) and dibenzosuberone (F). The standard enthalpies of vaporization Δ_vH^o or sublimation Δ_sH^o of A-F and 5,7-dihydro-6H-dibenzo[a,c]cyclohepten-6-one (G) were obtained from the temperature function of the vapor pressure measured in a flow system. Enthalpies of fusion Δ_mH of solid compounds were measured by DSC. From the enthalpies of formation of the gaseous compounds of A-G the values of their strain enthalpies were derived and structural effects discussed.

     

Thermochemistry of amineborane adduct formation of pyridine and picoline isomers

The enthalpy of reaction of pyridine, 2-, 3-, and 4-picoline with BH₃·THF and the enthalpy of solution of the same amines in THF were determined by reaction-solution calorimetry. From these data, the enthalpies of formation of the corresponding amineborane adducts in solution of THF were also determined. The results can be explained by considering the steric and inductive effects of the methyl group on the pyridine ring and the basicity of amines. The enthalpy of formation of the adducts in solution of THF correlates well with the available literature values of pK _a of amines also determined in THF, and the influence of the solvent on the basicity features of studied amines is verified.     

Thermochemistry of molecular complexes. 5. Molecular complexes of I2 with ethylbenzenes andn-alkylbenzenes

The enthalpies of formation and equilibrium constants are reported for molecular complexes of I₂ with five ethylbenzene and ninen-alkylbenzene donor molecules in CCl₄. The wavelength of maximum absorbance for each complex is also reported. For ethylbenzene donor molecules, the formation enthalpy and equilibrium constant for the complexes depend strongly on the number of ethyl groups attached to the benzene ring, but only weakly on the position of the groups. For then-alkylbenzene donor molecules, both the formation enthalpy and equilibrium constant for complex formation are indenpendent of the length of the alkyl chain. These results are consistent with previous observations on weak complexes of I₂ with substituted benzene donors.     

Thermochemistry of decomposition of manganese(II) oxalate dihydrate

Differential scanning calorimetry (DSC) has been used to determine the enthalpy of dehydration of manganese(II) oxalate dihydrate and the enthalpies of decomposition in nitrogen and in oxygen of the anhydrous oxalate. The thermodynamic data have been related to the activation energies reported in kinetic studies and to the mechanisms proposed for the thermal decomposition and oxidation processes.     

水合烟酸钡的合成、±结构表征和热化学性质

选择烟酸和氢氧化钡作为反应物, 利用室温固相合成方法, 借助于球磨技术, 合成了一种新的化合物——水合烟酸钡. 利用化学分析、元素分析、FTIR和X射线粉末衍射等方法确定了它的组成和结构为Ba(Nic)2·3H2O(s). 利用精密自动绝热热量计直接测定了此化合物在78-400 K温区的摩尔热容. 在热容曲线上出现了一个明显的吸热峰, 通过对热容曲线的解析, 得到了相变过程的峰温、相变焓和相变熵分别为(327.097±1.082) K、(16.793±0.084) kJ·mol-1和(51.340±0.164) J·K-1·mol-1. 将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp,m)对温度(T)的多项式方程, 并且在此基础上计算出了它的舒平热容值和各种热力学函数值. 另外, 依据Hess定律, 通过设计合理的热化学循环, 选择体积为100 mL、浓度为0.5 mol·L-1的盐酸作为量热溶剂, 利用等温环境溶解-反应热量计分别测量固相反应的反应物和产物在所选溶剂中的溶解焓, 利用溶解焓确定固相反应的反应焓为⊿rH0m=-(84.12±0.38) kJ·mol-1. 最后, 利用固相反应的反应焓和其它反应物和产物已知的热力学数据计算出水合烟酸钡的标准摩尔生成焓为⊿fH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90) kJ·mol-1.     

Thermochemistry of the complexes of some microelements and histidine

Solid complexes of M(His)₂Cl₂·nH₂O (M=Mn, Co, Ni, Cu) of MnCl₂·6H₂O, CoCl₂·6H₂O, NiCl₂·6H₂O, CuCl₂·2H₂O and L-α-histidine (His) have been prepared in 95% ethanol solution and characterized by elemental analyses, chemical analyses, IR and TG-DTG. The constant-volume combustion energies of the complexes have been determined by a rotating-bomb calorimeter. And the standard enthalpies of formation of the complexes have been calculated as well. This revised version was published online in August 2006 with corrections to the Cover Date.