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Journal of Thermal Analysis and Calorimetry
Authors: Xian'e Cia, Daichun Du, Youming Jin, and Yixiang Qian

Abstract  

N(C5F11)3 (Fluorint FC-70) has been chosen as the test material to compare the chemicophysical data obtained by static-sample and DSC methods. The normal boiling point, the molar enthalpy of vaporization, and the constants of the Antoine equation of fluorint FC-70 are reported. DSC can be developed into a simple and rapid routine instrument to determine the enthalpy of vaporization as well as the boiling point of liquid, particularly at relative high temperature.

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A miniaturized effusion cell adapted to a Sorption LKB microcalorimeter has been designed, built and tested. Vaporization is performed isothermally into a vacuum through a small orifice permitting a vapour pressure very close to the equilibrium values. The cell has been tested by measuring the enthalpies of vaporization at 298.15 K of reference liquid compounds (water, benzene, propanol-1, propanol-2) with a reproducibility better than 1%. Enthalpies of vaporization of butanol-1 and deuterated water have also been determined.

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Journal of Thermal Analysis and Calorimetry
Authors: V. Ovchinnikov, E. Sagadeev, L. Lapteva, L. Khasieva, M. Alikberov, E. Sitnikova, I. Antipin, I. Stoikov, and A. Konovalov

Abstract  

The enthalpies of vaporization of different classes of phosphorylated alcohols and amines were determined from their enthalpies of solution in hexane and carbon tetrachloride. The enthalpies of specific (hydrogen-bond) interaction with the solvents (chloroform and pyridine) of derivatives containing X-H groups (X=O or N) in the α-position to the P=O group were determined. The results were explained in terms of the spatial structure of such compounds.

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Thermochemistry of heteroatomic compounds

VII. Enthalpies of solution, vaporization and solvation of three-coordinated arsenic derivatives

Journal of Thermal Analysis and Calorimetry
Authors: V. Ovchinnikov, T. Makeeva, L. Lapteva, V. Valiullina, L. Pilishkina, and A. Konovalov

Abstract  

The enthalpies of vaporization of different classes three-coordinated arsenic compounds have been determined according to their enthalpies of solution in hexane and molar refraction. The enthalpies of solvation of cyclic and acyclic As(III)-derivatives in hexane, carbon tetrachloride,p-xylene and pyridine are obtained and discussed.

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Abstract  

Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350°C in a flowing atmosphere of nitrogen. The heating rate and the flow rate were varied. The DTA shows a melting at around 80°C and boiling point range from 212 to 251°C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between them.p. and the normalb.p. Evaporation is limited to the surface area, which is a constant in the crucible holding the sample. The DTG plot shows clearly a zero order process which is consistent with the process of evaporation. The enthalpy of vaporization (Δvap H) calculated by Trouton's rule is found to be in the range of 42.7–46.1 kJ mol−1. TheE act for the zero order reaction is in the range of 81.8–87.0 kJ mol−1 and is calculated by use of the derivative method. The value ofE act is about twice that for ΔH vap in Ibuprofen and differs from other compounds, whereE act ≈Δ H vap. It is suggested that the Ibuprofen molecule is existing as a dimer in the liquid state and dissociates to a monomer in the vapor state.

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Abstract  

The standard (p 0=0.1 MPa) molar enthalpies of formation, in the condensed phase, of nine linear-alkyl substituted thiophenes, six in position 2- and three in position 3-, at T=298.15 K, were derived from the standard massic energies of combustion, in oxygen, to yield CO2(g) and H2SO4·115H2O(aq), measured by rotating-bomb combustion calorimetry. The standard molar enthalpies of vaporization of these compounds were measured by high temperature Calvet Microcalorimetry, so their standard molar enthalpies of formation, in the gaseous phase, were derived. The results are discussed in terms of structural contributions to the energetics of the alkyl-substituted thiophenes, and empirical correlations are suggested for the estimation of the standard molar enthalpies of formation, at T=298.15 K, for 2- and 3-alkyl-substituted thiophenes, both in the condensed and in the gaseous phases.

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Abstract  

The standard (p o = 0.1 MPa) molar enthalpies of formation
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $${{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{l),}}$$ \end{document}
of the liquid 2-methylfuran, 5-methyl-2-acetylfuran and 5-methyl-2-furaldehyde were derived from the standard molar energies 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 enthalpies of vaporization of the three compounds. The standard (p o = 0.1 MPa) molar enthalpies of formation of the compounds, in the gaseous phase, at T = 298.15 K have been derived from the corresponding standard molar enthalpies of formation in the liquid phase and the standard molar enthalpies of vaporization. The results obtained were −(76.4 ± 1.2), −(253.9 ± 1.9), and −(196.8 ± 1.8) kJ mol−1, for 2-methylfuran, 5-methyl-2-acetylfuran, and 5-methyl-2-furaldehyde, respectively.
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Journal of Thermal Analysis and Calorimetry
Authors: Maria Ribeiro da Silva, Joana Cabral, Chelsea Givens, Stephanie Keown, and W. Acree

Abstract  

The standard (p 0=0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T-298.15 K, for 2,5-dimethylpyrazine (2,5-DMePz) and for the two dimethylpyrazine-N,N′-dioxide derivatives, 2,3-dimethylpyrazine-1,4-dioxide (2,3-DMePzDO) and 2,5-dimethylpyrazine-1,4-dioxide (2,5-DMePzDO), were derived from the measurements of standard massic energies of combustion, using a static bomb calorimeter, and from the standard molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry. The mean values for the molar dissociation enthalpy of the nitrogen-oxygen bonds, 〈DH m 0〉(N-O), were derived for both N,N′-dioxide compounds. These values are discussed in terms of the molecular structure of the two N,N′-dioxide derivatives and compared with 〈DH m 0〉(N-O) values previously obtained for other N-oxide derivatives.

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Abstract  

The standard (p 0=0.1 MPa) molar enthalpy of formation, Δf H m 0(l)=169.8±2.6 kJ mol−1, of the liquid 3-bromoquinoline was derived from its standard molar energy of combustion, in oxygen, to yield CO2(g), N2(g) and HBr·600H2O(l), at T=298.15 K, measured by rotating bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpy of vaporization of the compound, Δ1 g H m 0=70.7±2.3 kJ mol−1. These two thermodynamic parameters yielded the standard molar enthalpy of formation, in the gaseous phase, at T=298.15 K, Δf H m 0(g)=240.5±3.5 kJ mol−1.

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