首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   23篇
  国内免费   1篇
  完全免费   2篇
  化学   26篇
  2008年   1篇
  2006年   1篇
  2005年   1篇
  2003年   1篇
  2002年   1篇
  1999年   2篇
  1998年   2篇
  1997年   2篇
  1996年   1篇
  1995年   4篇
  1994年   1篇
  1992年   2篇
  1991年   1篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
排序方式: 共有26条查询结果,搜索用时 68 毫秒
1.
    
Molar excess volumes V E at 25°C have been determined by vibrating-tube densimetry, as a function of mole fraction x for different series of an alkanoate (H 2m+1 C m COOC n H 2n+1 )+cyclohexane. Three types of alkanoates were investigated, i.e., methanoates (m=0, with n=3 and 4), ethanoates (m=1, with n=2, 3, and 4) and propanoates (m=2, with n=1, 2, and 3). In addition, a Picker flow calorimeter was used to obtain molar excess heat capacities C p E at constant pressure at the same temperature. V E is positive for all systems and rather symmetric, with V E (x=0.5) amounting to almost identical values in a series of mixtures containing an alkanoate isomer of same formula (say C4H8O2, C5H10O2, or C6H12O2). The composition dependence of C p E is rather unusual in that two more or less marked minima are observed for most of the mixtures, especially when the alkanoate is a methanoate or an ethanoate. These results are discussed in terms of possible changes in conformation of both the ester and cyclohexane.  相似文献
2.
    
Excess volumes, excess isentropic compressions and excess isobaric heat capacities for binary liquid mixtures of methanol with ethanol, 1-propanol and 1-butanol have been determined at 25° C. These thermodynamic functions are smaller than those for alkanol + water mixtures and are correlated with the difference in the alkyl chain length in two of the alkanol molecules. The behavior of the component molecules in solution is found to be similar to that in the pure liquid. The excess isentropic compressions of methanol + 1-butanol show an S-shaped concentration dependence with a positive lobe in the methanol rich range and a negative lobe in the methanol poor range, which resembles that of the excess Gibbs energy reported by Polak et al.  相似文献
3.
    
The heat capacities and volumes for binary mixtures of benzonitrile with cyclohexane were determined at 10, 25, and 45°C. The dependence of the molar excess heat capacities on temperature and composition are interpreted in terms of the thermal relaxation of associated benzonitrile molecules into monomeric species.To whom correspondence should be addressed.  相似文献
4.
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
5.
Excess enthalpies, and heat capacities derived therefrom, have been obtained between 25 and 65 or 75°C at a constant concentration for cyclohexane and octamethylcyclotetrasiloxane mixed with normal hexadecane and with a highly branched C16 isomer, 2,2,4,4,6,8,8-heptamethylnonane, and also forcis-andtrans-decalin mixed withn-C16. Theh E values withn-C16 are positive and much larger than with the branched-C16. They decrease rapidly withT so thatc p E is large and negative. These results imply the presence of orientational order in then-C16, which is destroyed on mixing with the other component and which decreases withT. Theh E fortrans-decalin+n-C16 is much smaller than forcis-decalin+n-C16, and becomes negative with increase ofT. This change of sign, which is unexplained by current theory, is interpreted as due to an interference of the flat, plateliketrans-decalin molecule with the molecular motion of then-C16 chain.  相似文献
6.
A simple equation has been derived relating the temperature dependence of activity functions with excess enthalpies and excess heat capacities. Using experimentally determined parameters at 298.15°K, it is possible to predict osmotic coefficients and mean activity coefficients of alkali halides in water up to 1 m from 273°K to about 350°K. In general, the predicted functions agree with the measured values within the uncertainty of the activity data. An equation is also given for the pressure dependence of the excess free energies, but it was not possible to check the limitation of this equation due to lack of activity data at various pressures.To whom correspondence should be addressed.  相似文献
7.
8.
南照东  谭志诚  邢军 《中国化学》2005,23(10):1297-1302
Molar heat capacities of n-butanol and the azeotropic mixture in the binary system [water (x=0.716) plus n-butanol (x=0.284)] were measured with an adiabatic calorimeter in a temperature range from 78 to 320 K. The functions of the heat capacity with respect to thermodynamic temperature were estabhshed for the azeotropic mixture. A glass transition was observed at (111.9±1.2) K. The phase transitions took place at (179.26±0.77) and (269.69±0.14) K corresponding to the solid-hquid phase transitions of n-butanol and water, respectively. The phase-transition enthalpy and entropy of water were calculated. A thermodynamic function of excess molar heat capacity with respect to temperature was estabhshed, which took account of physical mixing, destructions of self-association and cross-association for n-butanol and water, respectively. The thermodynamic functions and the excess thermodynamic ones of the binary systems relative to 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity and the calculated excess heat capacity with respect to temperature.  相似文献
9.
10.
In the search of a useful method for determining excess enthalpies as a function of temperature Calvet calorimetry was employed. To this end, excess molar enthalpies
at 298.15 and 333.15 K and excess molar heat capacities
within 283.15–333.15 K were determined for the 1-decanol+n-decane system over the whole composition range. An isothermal flow Calvet-type calorimeter was used for
measurements, whereas
were determined by means of a Setaram Micro DSC calorimeter. Excess enthalpies within 283.15–333.15 K were indirectly obtained through the integration of
(T) data using
at 298.15 K. The results obtained at 333.15 K agreed with those determined directly, implying the thermodynamic consistency of the measured data and, therefore, the reliability of the indirect method.  相似文献
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号