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Abstract  

The excess molar enthalpies of (1–x)water+x1,4-dioxane have been measured at four different temperatures. All the mixtures showed negative enthalpies in the range of low mole fraction but positive ones in the range of high mole fraction of 1,4-dioxane. Excess enthalpies were increased with increasing temperature except those of at 278.15 K. Partial molar enthalpies have maximum around x=0.13 and minimum around x=0.75. Three different behaviors for the concentration dependence of partial molar enthalpies were observed for all temperature. Theoretical calculations of molecular interactions of three characteristic concentrations were carried out using the molecular orbital method.

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Journal of Thermal Analysis and Calorimetry
Authors:
Xing Xiaoling
,
Xue Liang
,
Zhao Fengqi
,
Yi Jianhua
,
Gao Hongxu
,
Xu Siyu
,
Pei Qing
,
Hao Haixia
, and
Hu Rongzu

empirical formulae describing the concentration b versus the enthalpy of dissolution (Δ diss H ), relative partial molar enthalpy (Δ diss H partial ), relative apparent molar enthalpy (Δ diss H apparent ), and the enthalpy of dilution (Δ dil H 1

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.426 With the help of the values of b and Δ sol H m in Table 4 , the empirical formula of enthalpy describing the b versus Δ sol H m relation is obtained: The empirical formulae of relative apparent molar enthalpy and relative partial molar enthalpy

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Abstract  

Excess enthalpies of sixteen binary mixtures between one each of methyl methylthiomethyl sulfoxide (MMTSO) and dimethyl sulfoxide (DMSO) and one of ketone {CH3CO(CH2)nCH3, n=0 to 6 and CH3COC6H5} have been determined at 298.15 K. All the mixtures showed positive excess enthalpies over the whole range of mole fractions. Excess enthalpies of ketone+MMTSO or DMSO increased with increasing the number of methylene radicals in the methyl alkyl ketone molecules. Excess enthalpies of MMTSO+ketone are smaller than those of DMSO+ketone for the same ketone mixtures. The limiting excess partial molar enthalpies of the ketone, H 1 E,∞, in all the mixtures with MMTSO were smaller than those of DMSO. Linear relationships were obtained between limiting excess partial molar enthalpies and the number of methylene groups except 2-propanone.

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Abstract  

The partial molar enthalpies of mixing of NaHSO4 and KHSO4 have been measured at 528 K by dropping samples of pure compounds into molten mixtures of NaHSO4 and KHSO4 in Calvet calorimeter. From these values the molar enthalpy of mixing has been deduced. The same method has been used for the determination of the heat capacity of the two pure compounds in the solid and liquid states. The phase diagram of this system has been confirmed by conductometric and thermal analysis methods. By an optimization method the excess entropy of the liquid mixtures was also calculated.

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Abstract  

Literature data on molar excess enthalpies and molar excess Gibbs energies, liquid-liquid equilibria, activity coefficients at infinite dilution and partial molar enthalpies at infinite dilution of binary mixtures of n-perfluoroalkanes (C5−C8)+n-alkanes (C5−C8) and of n-perfluorohexane-linear monoethers of general formula, CH3(CH2)m-O-(CH2)n-CH3 (m,n=1–4), are treated in the framework of DISQUAC, an extended quasichemical group contribution theory. The systems are characterized by two or three types of contact surfaces: aliphatic (CH3, CH2, CH and C groups), fluorine (F group) and oxygen (O group). Using a limited number of adjusted contact interchange energies parameters, structure dependent, the model provides a fairly consistent description of the thermodynamic properties as a function of concentration. The model may serve to predict missing data.

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Abstract  

The excess molar enthalpies and volumes have been determined for the binary system (water+octan-1-ol or +octan-2-ol) by means of direct calorimetric and densimetric measurements in the miscibility range. The experimental data were described through a Redlich-Kister type equation. For excess enthalpies a sigmoidal shape is predicted,while excess volumes are negative except for a little positive queue observed for(water+octan-1-ol) system at very low water content. Also the partial molar enthalpies of solution and the partial molar volumes of water in the two isomeric octanols at infinite dilution have been evaluated and discussed. A comparison is made between excess enthalpies and excess free energies calculated by the UNIFAC method.

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Abstract  

Excess enthalpies (H E) of 17 binary mixtures of o- and m-isomers of dichlorobenzene, difluorobenzene, methoxymethylbenzene, dimethylbenzene, dimethoxybenzene, aminofluorobenzene, fluoronitrobenzene, diethylbenzene, chlorofluorobenzene, fluoroiodobenzene, bromofluorobenzene, chloromethylbenzene, fluoromethylbenzene, bromomethylbenzene, iodomethylbenzene, fluoromethoxybenzene, dibromobenzene at 298.15 K were measured. All excess enthalpies measured were very small, and those of o-+m-isomers of aminofluorobenzene, dibromobenzene and iodomethylbenzene were negative but 14 other binary mixtures of isomers were positive over the whole range of mole fractions. H E of o-+m-isomers of dimethoxybenzene showed the largest enthalpic instability and those of aminofluorobenzene showed the largest enthalpic stability. There was a correlation between dipole–dipole interaction, dipole–induced dipole interaction or entropies of vaporization and excess partial molar enthalpies at infinite dilution.

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Abstract  

Uranium oxides are known as nonstoichiometric compounds whose composition changes according to external conditions such as temperature and oxygen partial pressure. The change of composition caused by the formation of defect structure results in a change of their properties. In this paper, the compositional changes of UO2 and doped UO2 [(U, M)O2; M=La, Ti, Pu, Th, Nb, Cr, etc.] and also those of other uranium oxides (U4O9, U3O8) are shown against oxygen partial pressure. From the results of doped UO2, it is concluded that the valence control rule holds to a first approximation. The defect structures are estimated both from log x vs. log Po2 (x: deviation from the stoichiometric composition and Po2: oxygen partial pressure) and log vs. log Po2 (: electrical conductivity) relations. The defect structures of UO2 and doped UO2 are derived based on the Willis model for UO2+x. The detect structure of U4O9 phase is similar to that of UO2+x, but the defect structures of U3O8 phase are complicated due to the existence of many higher-order phase transitions. The thermodynamic data such as the partial molar enthalpy and entropy and the heat capacity are important to characterize the defect structure. The high temperature heat capacities of UO2 doped with Gd show pronounced increases at high temperatures the onset temperature decreases as the dopant content increases. The increase of heat capacity is interpreted to be due to the formation of lattice defects. The heat capacity measurements on U4O9 and U3O8 clucidate the presence of the phase transition. The mechanisms of these phase transitions are discussed.

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change in enthalpy of solution, is the enthalpy of pure component 2 and is the partial molar enthalpy of component 2. It is noted that one can not determine the absolute values of enthalpy but the difference between the enthalpic content of the

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