Excess isobaric heat capacities for water + alkanol mixtures at 298.15 K

Excess isobaric heat capacities for water + methanol, + ethanol, + 1-propanol and + 1-butanol mixtures were measured at 298.15 K. The apparatus used in this study was a flow microcalorimeter designed and constructed in our laboratory recently, which can determine excess heat capacities directly by a method different from that of a Picker type calorimeter.The results obtained are roughly in agreement with the literature values, except for the water + 1-propanol mixture. This discrepancy from the literature values may arise from the thermodynamic instability of the water + alkanol mixture with the long-chain alkyl group and the difference in the procedure for obtaining the excess heat capacity.     

Excess heat capacities of binary mixtures of tetrachloromethane with some aromatic liquids at 298.15 K

A Picker flow calorimeter was used to obtain excess heat capacities at 298.15 K for mixtures of tetrachloromethane + toluene, + each of the three xylenes, + ethylbenzene, + mesitylene, and + chlorobenzene. The excess heat capacities are positive in all cases, with the exception of tetrachloromethane + mesitylene. Comparison of the results with values calculated from a “regular associated solution” model supports the view that complex formation occurs in these mixtures.     

Thermodynamic characterization of the mixture (1-butanol + iso-octane): Densities,viscosities, and isobaric heat capacities at high pressures

The densities at high pressures of 1-butanol and iso-octane were measured in the range (0.1 to 140) MPa at seven different temperatures, from (273.15 to 333.15) K, and their mixtures were measured in the range (0.1 to 50) MPa at four different temperatures, from (273.15 to 333.15) K. The measurements were performed in a high-pressure vibrating tube densimeter. The pressure–volume–temperature behavior of these compounds and their mixtures was evaluated accurately over a wide range of temperatures and pressures. The data were successfully correlated with the empirical Tamman–Tait equation. The experimental data and the correlations were used to study the behavior and the influence of temperature and pressure on the isothermal compressibility and the isobaric thermal expansivity.Also, the isobaric heat capacities were measured over the range (0.1 to 25) MPa at two different temperatures (293.15 and 313.15) K for the pure compounds and their mixtures. The measurements were performed in a high-pressure automated flow calorimeter. The excess molar heat capacities were assessed for the mixture and a positive deviation from the ideality was obtained.     

Thermodynamic properties of new heat pump working pairs: 1,3-Dimethylimidazolium dimethylphosphate and water,ethanol and methanol

Ionic liquid 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) + water/ethanol/methanol mixtures exhibit properties which render them suitable as candidates for working pairs in industrial applications of absorption heat pumps or chillers. In this paper, the thermodynamic properties including vapor pressure, density, viscosity, heat capacity as well as excess enthalpy of these binary systems were measured at various temperatures with different ionic liquid concentrations. The thermodynamic properties were correlated by different equations, respectively. The correlated values were significantly consistent with the experimental ones. In conclusion, the vapor–liquid equilibrium (VLE) data indicated that the vapor pressures of the three solvents in [MMIM][DMP] displayed a considerable negative deviation from Raoult's law, and the excess enthalpies of the three binary systems are negative. These characteristics are necessary and important for an absorption working pair.     

Enthalpies and heat capacities of hematoporphyrin solutions in N,N-dimethylformamide and octanol-1

Heat effects of the dissolution of hematoporphyrin tetramethyl ether are measured on a variable-temperature calorimeter for the first time in N,N-dimethylformamide and octanol-1 in the temperature range of 298 to 318 K. Standard enthalpies and heat capacities of dissolution of bioligand are calculated and compared to data obtained earlier for deuteroporphyrin dimethyl ether and ethyl acetate. Partial molar heat capacities of hematoporhyrin are determined at infinite dilution using data from differential scanning calorimetry.     

Excess volumes and excess heat capacities of nitromethane+(1-propanol or 2-propanol)

Densities and heat capacities of binary mixtures containing nitromethane+(1-propanol or 2-propanol) were determined at the temperatures (288.15, 293.15, 298.15, and 308.15) K and atmospheric pressure, over the whole composition range. Excess molar volumes and excess molar isobaric heat capacities were calculated from the results thus obtained. The effect of specific interactions on the excess properties, and the dependence on the position of the OH group in the alkanol, are analysed.     

Thermodynamic properties of biofuels: Heat capacities of binary mixtures containing ethanol and hydrocarbons up to 20 MPa and the pure compounds using a new flow calorimeter

Heat capacities are of great significance in the design of new processes and the improvement of existing ones in R&D in production plants as well as the adaptation of new products, in this case, biofuels to their use in a variety of engines and technical devices. An automated flow calorimeter has been developed for the accurate measurement of isobaric heat capacities for pure compounds and mixtures over the range (250 to 400) K and (0 to 20) MPa. In this paper, isobaric heat capacities for heptane, ethanol and the binary mixtures of ethanol with heptane and toluene are reported.     

Thermodynamics of aqueous mixtures of nonelectrolytes. III. Compressibilities and isochoric heat capacities of water-n-alcohol mixtures at 25°C

Speeds of ultrasound in binary mixtures of water with methanol, ethanol, and 1-propanol were measured at 25°C over the whole composition range by a pulseecho-overlap method. Excess isentropic compressibilities, excess isothermal compressibilities and excess isochoric heat capacities were derived from the results in combination with the results of our previous studies of thermal expansibilities and isobaric heat capacities.Publication issued as NRCC No. 19497     

Molar heat capacities for (1-butanol + 1,4-butanediol, 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol) as function of temperature

The isobaric molar heat capacities for the binary mixtures (1-butanol + 1,4-butanediol) were determined in the temperature range from (293 to 353) K from measurements of isobaric specific heat capacity in a differential scanning calorimeter. The composition dependencies of the excess molar isobaric heat capacities obtained from the experimental results were fitted by the Redlich-Kister polynomials. Above T = 303.15 K, the excess isobaric molar heat capacities are negative over the whole composition range and absolute values increase with temperature. For temperatures (293.15 and 298.15) K, the excess values show S-shaped character. These excesses are however in general very small; at the temperature 298.15 K smaller than 0.1 J · K⁻¹ · mol⁻¹.Additionally, the isobaric molar heat capacities of 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol were determined over a similar temperature range. The experimental data for all diols are compared with available literature data and values estimated from group additivity.     

Volumes and heat capacities of binary liquid mixtures of water—sulfolane and water—hexamethylphosphotriamide

Density and heat capacity measurements of water—sulfolane mixtures at 303.15 K and water—hexamethylphosphotriamide mixtures at 298.15 K have been performed over the whole composition range. Molar, excess, apparent molar volumes and heat capacities were calculated for the two systems. The trends of these functions are discussed in terms of specific interactions between the components of the solvent mixtures and the changes caused by the organic solvents on the water structure.     

Volumes and heat capacities of mixtures of dimethylformamide with several dialkylacetamides

Densities and heat capacities per unit volume of binary mixtures of dimethylformamide and a series of di-n-alkylacetamides have been measured and converted into excess molar volumes and heat capacities of the mixtures. In addition, the apparent and partial molar volumes and heat capacities of the various components have been evaluated. They vary smoothly with the mole fraction. The apparent molar heat capacities in the mixtures depend linearly on volume fraction, so that the partial molar heat capacities can be described using only one parameter for each mixture.     

Molar heat capacities for (2-methyl-2-butanol + heptane) mixtures and cyclopentanol at temperatures from (284 to 353) K

Isobaric specific heat capacities were measured for (2-methyl-2-butanol + heptane) mixtures and cyclopentanol within the temperature range from (284 to 353) K, and for 2-methyl-2-butanol in the (284 to 368) K temperature interval by means of a differential scanning calorimeter. The excess molar heat capacities were calculated from the experimental results. For the temperature range from (284 to 287) K, the excess molar heat capacity is S-shaped with negative values in the 2-methyl-2-butanol rich region and with small negative values at low alcohol concentrations at temperatures from (295 to 353) K. The excess molar heat capacities are positive for all compositions under test at temperatures from (288 to 294) K. The results are explained in terms of the influence of the molecular size and configuration of the alkanols on their self-association capability and of the change in molecular structure of the (2-methyl-2-butanol + heptane) mixtures. The differences between the temperature dependences of the heat capacities of the mixtures studied are qualitatively consistent with results obtained by Rappon et al. [M. Rappon, J.M. Greer, J. Mol. Liq. 33 (1987) 227–244; M. Rappon, J.A. Kaukinen, J. Mol. Liq. 38 (1988) 107–133; M. Rappon, R.M. Johns, J. Mol. Liq. 40 (1989) 155–179; M. Rappon, R.T. Syvitski, K.M. Ghazalli, J. Mol. Liq. 62 (1994) 159–179; M. Rappon, R.M. Johns, J. Mol. Liq. 80 (1999) 65–76; M. Rappon, S. Gillson, J. Mol. Liq. 128 (2006) 108–114].     

Excess heat capacities and excess volumes of binary liquid mixtures of chloroform with cyclic ethers at 298.15 K

Molar excess heat capacities at constant pressure, C^E_p, of binary liquid mixtures chloroform + oxolane, chloroform + 1,3-dioxolane, chloroform + oxane, and chloroform + 1,4-dioxane have been determined at 298.15 K from measurements of volumetric heat capacities in a Picker flow microcalorimeter. A precision of ±0.04 J K^?1 mole^? was achieved by using the stepwise procedure. Experimental molar excess heat capacities are compared with values derived from H^E results at different temperatures. Excess molar volumes, V^E, for the same systems at 298.15 K have been determined by measuring the density of the pure liquids and solutions with a high-precision digital flow densimeter.     

Heat capacities and entropies of liquid,high-melting-point polymers containing phenylene groups (PEEK,PC, and PET)

The heat capacity at constant pressure of liquid PEEK, poly(oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene), has been measured by scanning calorimetry from 420 to 680 K, and that of PC, poly(4,4′-isopropylidenediphenylene carbonate), from 325 to 610 K. These new data were combined with data-bank data for PC and PET, poly(ethylene terephthalate), over wide temperature ranges. An addition scheme for liquid heat capacities of similar macromolecules has been obtained. In addition, values of absolute entropy, residual entropy for the glassy state, enthalpy, and Gibbs function are estimated for these three polymers. Both melting and glass transition temperatures have been confirmed. The heat capacity increases at the glass transition temperature have been determined by making use of previously calculated solid-state heat capacities.     

Excess molar enthalpies and excess molar heat capacities of (2-butanone + cyclohexane,or methylcyclohexane,or benzene,or toluene,or chlorobenzene,or cyclohexanone) atT = 298.15 K

Excess molar enthalpies of (2- butanone  +  cyclohexane, or methylcyclohexane, or toluene, or chlorobenzene, or cyclohexanone) and excess molar heat capacities of (2- butanone  +  benzene, or toluene, or chlorobenzene, or cyclohexanone) were measured atT =  298.15 K. Aliphatic systems were endothermic and the chlorobenzene system was exothermic. On the other hand, the toluene system changed sign to be S-shaped similar to the benzene system reported by Kiyohara et al. The values of excess molar enthalpies of the present mixtures were slightly larger than the corresponding mixtures of cyclohexanone already reported. Excess molar heat capacities of aromatic systems were characteristically S-shaped for the mixture containing aromatics. The values of the present mixtures were less than the corresponding mixtures of cyclohexanone. The mixture (2-butanone  +  cyclohexanone) was endothermic forH_m^E and negative for C_p,m^E.     

Heat capacities of binary cycloalkane mixtures at 298.15 K

Volumetric heat capacities of the six binary mixtures formed from cyclopentane, cyclohexane, cycloheptane and cyclooctane were determined at 298.15 K in a Picker flow microcalorimeter. Excess heat capacities obtained from the results are compred with the temperature variation of excess enthalpies from the literature.     

Low-temperature heat capacities and derived thermodynamic functions of cyclohexane

The low-temperature heat capacities of cyclohexane were measured in the temperature range from 78 to 350 K by means of an automatic adiabatic calorimeter equipped with a new sample container adapted to measure heat capacities of liquids. The sample container was described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on water. The deviations of experimental heat capacities from the corresponding smoothed values lie within ±0.3%, while the inaccuracy is within ±0.4%, compared with the reference data in the whole experimental temperature range. Two kinds of phase transitions were found at 186.065 and 279.684 K corresponding solid-solid and solid-liquid phase transitions, respectively. The entropy and enthalpy of the phase transition, as well as the thermodynamic functions {H_(T)-H _{298.15 K}} and {S _(T)-S_{298.15 K}}, were derived from the heat capacity data. The mass fraction purity of cyclohexane sample used in the present calorimetric study was determined to be 99.9965% by fraction melting approach. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heat capacities of binary mixtures of n-heptane with hexane isomers

Volumetric heat capacities were measured for binary mixtures of n-heptane with n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane at 298.15 K in a Picker flow microcalorimeter. The results were combined with previously published excess molar volumes to obtain excess molar isobaric heat capacities. Use of the Flory theory of mixtures to interpret the latter is discussed.     

水-乙醇二元体系共沸混合物的热力学研究

用全自动低温绝热量热计测定了水、乙醇以及水和乙醇组成的共沸混合物在不同温区的摩尔热容Cp,m. 建立了共沸混合物Cp,m与温度T的函数关系.结果表明,水和乙醇组成的共沸混合物在98.496 K发生玻璃态转化,在158.939 K 和270.95 K发生固-液相变.获得了其相应的相变焓和相变熵.计算了以298.15 K为基准的该共沸混合物的热力学函数和超额热力学函数.     

Flow microcalorimeter for heat capacities of solutions

A new type of flow microcalorimeter for measuring heat capacities at constant pressure of liquids and solutions was constructed. This calorimeter is the similar in design to Picker's except for the flow system, which consists of two syringe type of pumps and two flowing paths in each flow cell. It was found that the magnitude of heat loss from cells depended on liquids themselves used and the flow rates of sample liquids. The molar heat capacities, C_p of benzene and ethanol were determined relative to those of cyclohexane and water, respectively. The excess molar heat capacities, C_p(E) for the systems of benzene + cyclohexane and water + ethanol were also determined at 298.15K by the direct mixing method. An inaccuracy for C_p(E) was estimated to be within ± 1%.