Low-temperature heat capacities and standard molar enthalpy of formation of N-methylnorephedrine C11H17NO（s）

This paper reports that low-temperature heat capacities of N-methylnorephedrine C11H17NO（s） have been measured by a precision automated adiabatic calorimeter over the temperature range from T=78K to T=400K. A solid to liquid phase transition of the compound was found in the heat capacity curve in the temperature range of T=342-364 K. The peak temperature, molar enthalpy and entropy of fusion of the substance were determined. The experimental values of the molar heat capacities in the temperature regions of T=78-342 K and T=364-400 K were fitted to two poly- nomial equations of heat capacities with the reduced temperatures by least squares method. The smoothed molar heat capacities and thermodynamic functions of N-methylnorephedrine C11H17NO（s） relative to the standard refer- ence temperature 298.15 K were calculated based on the fitted polynomials and tabulated with an interval of 5 K. The constant-volume energy of combustion of the compound at T=298.15 K was measured by means of an isoperibol precision oxygen-bomb combustion calorimeter. The standard molar enthalpy of combustion of the sample was calculated. The standard molar enthalpy of formation of the compound was determined from the combustion enthalpy and other auxiliary thermodynamic data through a Hess thermochemical cycle.     

Low-temperature heat capacities and standard molar enthalpy of formation of 4-（2-aminoethyl）-phenol （C8H11NO）

This paper reports that low-temperature heat capacities of 4-（2-aminoethyl）-phenol （C8H11NO） are measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 400 K. A polynomial equation of heat capacities as a function of the temperature was fitted by the least square method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15K were calculated and tabulated at the interval of 5K. The energy equivalent, εcalor, of the oxygen-bomb combustion calorimeter has been determined from 0.68g of NIST 39i benzoic acid to be εcalor=（14674.69±17.49）J·K^-1. The constant-volume energy of combustion of the compound at T=298.15 K was measured by a precision oxygen-bomb combustion calorimeter to be ΔcU=-（32374.25±12.93）J·g^-1. The standard molar enthalpy of combustion for the compound was calculated to be ΔcHm = -（4445.47 ± 1.77） kJ·mol^-1 according to the definition of enthalpy of combustion and other thermodynamic principles. Finally, the standard molar enthalpy of formation of the compound was derived to be ΔfHm（C8H11NO, s）=-（274.68 ±2.06） kJ·mol^-1, in accordance with Hess law.     

Low-temperature heat capacities and thermodynamic properties of n-undecylammonium bromide monohydrate C11H28BrNO(s)

Crystal structure of n-undecylammonium bromide monohydrate was determined by X-ray crystallography. Low-temperature heat capacities of the compound were measured by a precision automated adiabatic calorimeter over the temperature range from 78 to 390?K. Two solid–solid phase transitions were observed for the title compound. The temperatures, molar enthalpies, and entropies of the phase transitions were derived based on the analysis of heat–capacity curve. Two polynomial equations of heat capacities as a function of temperature were fitted by least-squares method. Based on the two polynomial equations, 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.     

Investigation on phase transitions of 1-decylammonium hydrochloride as the potential thermal energy storage material

1-Decylammonium hydrochloride was synthesized by the method of liquid phase synthesis. Chemical analysis, elemental analysis, and X-ray single crystal diffraction techniques were applied to characterize its composition and structure. Low-temperature heat capacities of the compounds were measured with a precision automated adiabatic calorimeter over the temperature range from 78 to 380?K. Three solid–solid phase transitions have been observed at the peak temperatures of 307.52?±?0.13, 325.02?±?0.19, and 327.26?±?0.07?K. The molar enthalpies and entropies of three phase transitions were determined based on the analysis of heat capacity curves. Experimental molar heat capacities were fitted to two polynomial equations of the heat capacities as a function of temperature by least square method. Smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15?K were calculated and tabulated at intervals of 5?K based on the fitted polynomials.     

Crystal structure and thermochemical properties of bis（1-octylammonium） tetrachlorochromate phase change materials

A new crystalline complex(C8 H17 NH3) 2 CdCl 4(s)(abbreviated as C8Cd(s)) is synthesized by liquid phase reaction.The crystal structure and composition of the complex are determined by single crystal X-ray diffraction,chemical analysis,and elementary analysis.It is triclinic,the space group is P-1 and Z = 2.The lattice potential energy of the title complex is calculated to be U POT(C 8 Cd(s))=978.83 kJ·mol-1 from crystallographic data.Low-temperature heat capacities of the complex are measured by using a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K.The temperature,molar enthalpy,and entropy of the phase transition for the complex are determined to be 307.3±0.15 K,10.15±0.23 kJ·mol-1,and 33.05±0.78 J·K-1 ·mol-1 respectively for the endothermic peak.Two polynomial equations of the heat capacities each as a function of temperature are fitted by using the leastsquare method.Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials.     

Crystal structure and thermochemical properties of phase change materials bis(1-octylammonium) tetrachlorochromate

A new crystalline complex (C₈H₁₇NH₃)₂CdCl₄(s) (abbreviated as C₈Cd(s)) is synthesized by liquid phase reaction. The crystal structure and composition of the complex are determined by single crystal X-ray diffraction, chemical analysis, and elementary analysis. It is triclinic, the space group is P-1 and Z = 2. The lattice potential energy of the title complex is calculated to be U_POT (C₈Cd(s))=978.83 kJ·mol^-1 from crystallographic data. Low-temperature heat capacities of the complex are measured by a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K. The temperature, molar enthalpy, and entropy of the phase transition for the complex are determined to be 307.3± 0.15 K, 10.15± 0.23 kJ·mol^-1, and 33.05± 0.78 J·K^-1·mol^-1 respectively for the endothermic peak. Two polynomial equations of the heat capacities each as a function of temperature are fitted by the least-square method. Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials.     

Lattice potential energy and standard molar enthalpy in the formation of 1-dodecylamine hydrobromide (1-C12H25NH3 ·Br)（s）

This paper reports that 1-dodecylamine hydrobromide (1--C₁₂H₂₅NH₃·Br)(s) has been synthesized using the liquid phase reaction method. The lattice potential energy of the compound 1--C₁₂H₂₅NH₃·Br and the ionic volume and radius of the 1--C₁₂H₂₅NH₃⁺ cation are obtained from the crystallographic data and other auxiliary thermodynamic data. The constant-volume energy of combustion of 1--C₁₂H₂₅NH₃·Br(s) is measured to be Δ_c U_m^o(1--C₁₂H₂₅NH₃·Br, s) =--(7369.03±3.28) kJ·mol^-1 by means of an RBC-II precision rotating-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of combustion of the compound is derived to be Δ_c H_m^o(1--C₁₂H₂₅NH₃·Br, s)=--(7384.52±3.28) kJ·mol ^{- 1} from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound is calculated to be Δ_f H_m^o(1--C₁₂H₂₅NH₃·Br, s)=--(1317.86±3.67) kJ·mol^-1 from the standard molar enthalpy of combustion of the title compound and other auxiliary thermodynamic quantities through a thermochemical cycle.     

Thermodynamic Properties of the First-Generation Hybrid Dendrimer with “Carbosilane Core/Phenylene Shell” Structure

The molar heat capacity of the first-generation hybrid dendrimer with a “carbosilane core/phenylene shell” structure was measured for the first time in the temperature range T = 6–600 K using a precise adiabatic vacuum calorimeter and DSC. In the above temperature interval, the glass transition of the studied compound was observed, and its thermodynamic characteristics were determined. The standard thermodynamic functions (the enthalpy, the entropy, and the Gibbs energy) of the hybrid dendrimer were calculated over the range from T = 0 to 600 K using the experimentally determined heat capacity. The standard entropy of formation of the investigated dendrimer was evaluated at T = 298.15 K. The obtained thermodynamic properties of the studied hybrid dendrimer were compared and discussed with the literature data for some of the first-generation organosilicon and pyridylphenylene dendrimers.     

Crystal structure and thermodynamic properties of phase change material bis(1-dodecylammonium) tetrachlorochromate (C12H25NH3)2CdCl4(s)

A novel complex bis(1-dodecylammonium) tetrachlorochromate (C₁₂H₂₅NH₃)₂CdCl₄(s) (abbreviated as C₁₂Cd(s)) was synthesized by liquid phase reaction. Crystal structure and composition of the complex were determined by X-ray crystallography, chemical analysis, and elemental analysis. It is triclinic, the space group is P?1 and Z = 2. Lattice potential energy (LPE) of the complex was calculated to be kJ·mol^?1 from crystallographic data. Low-temperature heat capacities were measured by a precise automatic adiabatic calorimeter over the temperature range from 78 to 370 K. The temperature, molar enthalpy, and entropy of the phase transition of the complex were determined to be 331.88 ± 0.02 K, 55.79 ± 0.46 kJ·mol^?1, and 168.10 ± 1.38 J·K^?1·mol^?1, respectively. Two polynomial equations of the heat capacities as a function of temperature were fitted by least-square method. Smoothed heat capacities and thermodynamic functions of the complex were calculated.     

Thermodynamic properties of under-cooled silver melts

Differential scanning calorimeter technique combined with the traditional fluxing treatment was used to investigate the specific heat and related thermodynamic properties of under-cooled pure silver melts. The specific heat of the under-cooled melt showed a linear dependence on the temperature in the range of the obtained under-cooling from 0 to 198 K. The related thermodynamic properties of silver, such as the entropy change, the enthalpy change and the Gibbs free energy difference between the under-cooled...     

Standard molar enthalpies of formation of dimethylbenzophenones

The standard (p⁰ = 0.1 MPa) molar enthalpy of formation of 3,4‐dimethylbenzophenone was derived from the standard molar energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpy of sublimation of the compound. From these experimental parameters, the standard molar enthalpy of formation of 3,4‐dimethylbenzophenone, in the gaseous phase and at T = 298.15 K, was derived as ?(17.1 ± 2.9) kJ mol^?1. Density functional theory was used to investigate the gas‐phase molecular energetics of the 12 dimethylbenzophenones. Molecular geometries and vibrational frequencies were computed at the B3LYP/6‐31G(d) level of theory. The larger 6‐311+G(2d,2p) basis set was used to compute the energy of all dimethylbenzophenones and of the other compounds that were considered for the estimation of the standard molar enthalpies of formation at T = 298.15 K. The calculations show that the 2,2′‐ and 4,4′‐dimethylbenzophenones are the least and most stable isomers, respectively. Finally, the calculated enthalpy of formation of the benzophenone that was also studied experimentally, 3,4‐dimethylbenzophenone, is ?16.7 kJ mol^?1, which is in excellent agreement with the experimental result. Copyright © 2008 John Wiley & Sons, Ltd.     

Fusion curves and thermodynamic properties of carbon tetrachloride, chloroform, bromoform and silicon tetrachloride at pressure up to 3500 MPa

The fusion temperature as a function of pressure for carbon tetrachloride, chloroform, bromoform and silicon tetrachloride at pressures up to 3500MPa has been determined. The experimental data were fitted by the equation Tfus=T0（1 ＋ Δp/a1）^a2 exp（-a3Δp） and the changes of the maolar enthalpy and molar internal energy on fusion were calculated using the parameters of the fitted equation. Comparisons with the data from the literature show that the experimental data, parameters of fitted equations, changes of the molar enthalpy and molar internal energy are reliable.     

含乙酰胺基链苯并菲盘状液晶分子的电荷传输性质与热力学性质

在密度泛函理论B3LYP/6-31G**理论水平上,计算含乙酰胺基链苯并菲衍生物分子的电荷传输性质和热力学性质。研究结果显示,该分子的空穴传输性能明显好于电子传输性能。在298.15 K时,该分子的标准摩尔生成焓和生成自由能分别为-2338.79 kJ/mol和-1756.27 kJ/mol。     

含乙酰胺基链苯并菲盘状液晶分子的电荷传输性质与热力学性质

在密度泛函理论B3LYP／6－31G**理论水平上,计算含乙酰胺基链苯并菲衍生物分子的电荷传输性质和热力学性质.研究结果显示,该分子的空穴传输性能明显好于电子传输性能.在298.15 K时,该分子的标准摩尔生成焓和生成自由能分别为－2338.79 kJ／mol和－1756.27 kJ／mol。     

Calorimetric and computational study of 2H-1, 4-benzoxazin-3(4H)-one and of related species

The standard molar enthalpy of formation in the gas phase of 2H-1,4-benzoxazin-3(4H)-one was derived from the standard energy of combustion determined by static bomb combustion calorimetry in oxygen atmosphere and from the standard sublimation enthalpy determined by Calvet microcalorimetry. In addition, we report the results of a systematic theoretical study of the keto and enol tautomers in benzoxazinones and diones using density functional theory. The keto tautomers are computed to be more stable than the enols. Tautomerization energies are reported.     

Thermodynamic Study of Formamidinium Lead Iodide (CH5N2PbI3) from 5 to 357 K

In the present study, the molar heat capacity of solid formamidinium lead iodide (CH₅N₂PbI₃) was measured over the temperature range from 5 to 357 K using a precise automated adiabatic calorimeter. In the above temperature interval, three distinct phase transitions were found in ranges from 49 to 56 K, from 110 to 178 K, and from 264 to 277 K. The standard thermodynamic functions of the studied perovskite, namely the heat capacity C°_p(T), enthalpy [H⁰(T) − H⁰(0)], entropy S⁰(T), and [G°(T) − H°(0)]/T, were calculated for the temperature range from 0 to 345 K based on the experimental data. Herein, the results are discussed and compared with those available in the literature as measured by nonclassical methods.     

准稳态法测量液体比热容的实验研究

建立了准稳态量热计,通过测量纯水和正庚烷的比热容,对量热器进行了检验。比热容的测量结果与文献标准值比较,最大偏差不超过1.0％,表明量热器具有较高的精度和稳定性。在此基础上测量了含氧燃料添加剂碳酸二甲酯及可作为蓄热介质石腊的比热容,为混合燃料的设计和空调余热利用提供基础数据。     

Mg2Sn电子结构及热力学性质的第一性原理计算

采用基于第一性原理的赝势平面波方法系统地计算了Mg₂Sn基态的电子结构、弹性常数和热力学性质.计算结果表明Mg₂Sn的禁带宽度为0.1198eV.运用线性响应方法确定了声子色散关系和态密度,得出Mg₂Sn的热力学性质如等容比热和德拜温度.计算Mg₂Sn的热导率并与实验数据相比较. 关键词： 第一性原理 电子结构 弹性常数 热力学性质     

Barometric calorimeters

A barometric calorimeter technique has been developed to characterize the temporal evolution of combustion in confined explosions. By comparing pressure measurements for explosions in air versus nitrogen, one can make visible the gasdynamic (pressure) consequences of the exothermic energy release. The late-time chamber pressure measurement is used to evaluate the final mass-fraction of products produced by combustion. Combustion completeness varied from 50–89% over a wide range of stoichiometrics. A thermodynamic model of combustion in a calorimeter is proposed. The model was applied to the TNT-air system; chamber pressures varied between 1 bar and 1 kbar for fuel mass-fractions between 1 and 99%. Chamber temperature reached a maximum of 2.099 K at a fuel mass loading of 36%. We will show that combustion is a more-effective energy release mechanism for creating high temperatures and pressures in a confined explosion than the detonation mechanism.     

Enthalpy and heat capacity of the intermetallic compound CsBi<Subscript>2</Subscript> in the solid and liquid states

Enthalpy of solid and liquid intermetallic compound CsBi₂ in the temperature range of 430–1225 K was measured by massive isothermal drop calorimeter. Approximation equations were obtained, and isobaric heat capacity and enthalpy change on melting were determined. The tables of recommended values of caloric properties in the range from 298.15 K to 1225 K were developed. The experimental uncertainty of enthalpy and heat capacity measurements were estimated to be within 0.35 and 1.0%, respectively. The obtained results were compared with the calculations according to the laws of ideal solutions.