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31.
Using the Picker flow microcalorimeter, excess heat capacities have been obtained at 25°C throughout the concentration range for 2,2-dimethylbutane,n-hexane, and cyclohexane each mixed with a series of hexadecane isomers of increasing degrees of orientational order, as determined by depolarized Rayleigh scattering. The isomers are 2,2,4,4,6,8,8-heptamethylnonane, 6-, 4-, and 2-methylpentadecane, andn-hexadecane. Thec
p
E
values are negative, increasing rapidly in magnitude with increase of orientational order, and are not predicted by the Prigogine—Flory theory which neglects order. Values ofc
p
E
are obtained at 10, 25, and 55°C for cyclohexane +6-, 4-, and 2-methylpentadecane which with other literature data lead to the temperature dependence of the thermodynamic excess functions for cyclohexane solutions of the five C16 isomers. The excess enthalpy and entropy vary with the C16 isomer and with temperature, but the corresponding variation of the excess free energy is small, indicating a high degree of enthalpy-entropy compensation. This is consistent with a rapid decrease with temperature of orientational order in the C16 isomers. 相似文献
32.
Laurence E. Strong Thomas G. Copeland Margaret Darragh Carter Van Waes 《Journal of solution chemistry》1980,9(2):109-128
Conductivities of aqueous solutions ofortho-, meta-, andpara-toluic acids have been measured for the concentration range 0.1–2 millimolar and at 5° intervals from 5 to 100°C. At each temperature pK
a(m) andA
0 have been calculated using the paired ion model recently described by Fuoss. Thermodynamic parameters have been calculated for the ionization of each acid, and Walden products for the anions. Results are discussed in terms of contributions to acidity by enthalpy and entropy changes as well as by hydration of the various solute species. 相似文献
33.
34.
Kulova T. L. Karseeva E. I. Skundin A. M. Kachibaya E. I. Imnadze R. A. Paikidze T. V. 《Russian Journal of Electrochemistry》2004,40(5):494-499
A series of compounds with the general formula LiMn2 - x - y
Cr
x
Ni
y
O4, where x + y = 0.05, 0.5, or 1.0, is synthesized. It is shown that all these compounds are pure-phase spinels with parameter aequal to 0.8193-0.8236 nm. Doping a stoichiometric lithium-manganese spinel simultaneously with chromium and nickel makes the spinel structure stable. The initial specific capacity of a spinel depends on its doping degree. Doping LiMn2O4 with chromium and nickel simultaneously at an Mn : Cr : Ni ratio of 195 : 3 : 2 raises the spinel's specific capacity and reduces the cycling degradation. The change in the discharge capacity of LiMn1.95Cr0.03Ni0.02O4 electrodes cycled at 20, 0, and -14°C is determined. 相似文献
35.
36.
M. Fujisawa T. Matsushita Y. Matsui K. Akasaka T. Kimura 《Journal of Thermal Analysis and Calorimetry》2004,77(1):225-231
The heat capacities of binary aqueous solutions of 1,2-ethanediol, 1,2-propanediol and 1,2-butanediol were measured at temperatures
ranging from 283.15 to 338.15 K by differential scanning calorimetry. The partial molar heat capacities at the infinite dilution
were then calculated for the respective alkanediols. For 1,2-ethanediol or 1,2-propanediol, the partial molar heat capacities
at the infinite dilution of increased with increasing temperature. In contrast, the partial molar heat capacities of 1,2-butanediol
at the infinite dilution decreased with increasing temperature.
Heat capacity changes by dissolution of the alkanediols were also determined. Heat capacity changes caused by the dissolution
of 1,2-ethanediol or 1,2-propanediol were increase with increasing temperature. On the other hand, heat capacity changes caused
by the dissolution of 1,2-butanediol are decrease with increasing temperature. Thus our results indicated that the structural
changes of water caused by the dissolution of 1,2-butanediol differed from that of the two other alkanediols.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
37.
Using a precise technique of scanning microcalorimetry the heat capacity differences between water and dilute aqueous solutions of ethanol, n-propanol, n-butanol and n-pentanol were measured from 5 to 125°C and the partial molar heat capacities of these substances in water were determined. It was found that the heat capacity increment for alcohol disolved in water is proportional to the number of the-CH
2
–
groups and decrease with a temperature increase. The heat capacity increment of hydration of non-polar groups is shown to be positive and large at room temperature and decreases in magnitude as the temperature increases. In contrast, the heat capacity increment of hydration of polar groups is negative at room tempreature and increases as the temperature increases. From the temperature dependence of the heat capacity increment one can assume that the water molecules solvated by the non-polar groups of the alcohols behave in a non-cooperative manner. 相似文献
38.
Monuron (C9H11ClN2O; N,N-dimethyl-N′-(4-chlorophenyl) urea, CAS 150-68-5) was synthesized and the heat capacities of the compound were measured in the temperature range from 79 to 385 K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The enthalpy and entropy data of the compound relative to the reference temperature 298.15 K were derived based on the heat capacity data. The thermodynamic properties of the compound were further investigated through DSC and TG analysis. The melting point, the molar enthalpy, and entropy of fusion were determined to be 447.6±0.1 K, 29.3±0.2 kJ mol−1, and 65.4 J K−1 mol−1, respectively. 相似文献
39.
Russell G. Ross 《Journal of inclusion phenomena and macrocyclic chemistry》1990,8(1-2):227-233
The thermal conductivity and the heat capacity per unit volumec
p
have been measured for the urea-hexadecane inclusion compound using the transient hot-wire method. Measurements were made under isobaric conditions at a pressure of 0.1 GPa and in the temperature range of 100–300 K. There was evidence for a phase transition at a temperature of about 160 K, in reasonable agreement with previous work. For the high-temperature phase was independent of temperature within ±1%. The low-temperature phase showed a weak temperature dependence, with (d In/d InT)
p
= –0.13. It was inferred that interaction between acoustic phonons and low-frequency vibrational excitations of the guest molecules made a major contribution to the thermal resistivity. For the quantityc
p
a weak maximum was observed in the region of the phase transition temperature.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena. 相似文献
40.
Scanning calorimetric methods permit determination of heat capacities at high temperatures up to 1600°C. For disk systems
with power compensation application limits are in order of 700°C, and for cylindrical systems with electrical calibration
up to 1000°C. For the high temperature range above 1000°C DSC plates and a cylindrical calorimetric systems based on the CALVET
principle ('MULTI HTC’) are known. For cylindrical calorimetric systems the precision of the Cp data is between 2 and 5% even
at high temperatures without any requirements on the kind and shape of samples. These results are better than data provided
by DSC plate systems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献