共查询到20条相似文献,搜索用时 46 毫秒
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溶液的蒸气压下降是溶液的重要性质之一,它导致了溶液的沸点升高和凝固点降低,是师专、医药专科、大一基础化学教学的重要内容之一,但未安排这个实验。过去我们在教学中通过课堂演示实验,给学生以感性认识。 相似文献
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长期以来,稀溶液中溶剂A的化学势为μA(1)=μ^*A(1)+RTlnxA,溶质B的化学势为μB(溶质)=μ^ΞB(溶质)+RTln(bB/b^Ξ),两式使用了不同的组成变量:溶剂的摩尔分数xA,溶质的质量摩尔浓度bB。按规定,溶液的组成变量应选用bB,故本文介绍了导出理想稀溶液中μA(1)=μ^*A(1)-RTMA∑BbB的方法,并从此式出发推导出稀溶液的依数性。 相似文献
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A two-dimensional theoretical model for solids-coated, or "armored," bubbles shows how the armor can support a liquid-vapor interface of reduced or reversed curvature between the particles, giving the bubble zero or even negative capillary pressure. The inward capillary force pulling the particles into the center of the bubble are balanced by large contact forces between the particles in the armor. Thus the bubble is stabilized against dissolution of gas into surrounding liquid, which otherwise would rapidly collapse the bubble. The stresses between particles in such cases are large and could drive sintering of the particles into a rigid framework. Earlier work on solids-coated bubbles assumed that solids can freely enter or leave the bubble surface as the bubble shrinks or expands. In such a case, armored bubbles would not be stable to gas dissolution into surrounding liquid. A new free-energy analysis, however, suggests that a shrunken bubble would not spontaneously expel a solid particle from its armor to relieve stress and allow the bubble to shrink further. Implications and limitations of the theory are discussed. Copyright 1999 Academic Press. 相似文献
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Y. H. Zhang J. Meng X. Q. Zhang Hui Li C. A. Taft 《International journal of quantum chemistry》2009,109(6):1385-1395
Well‐ordered single, double/four parallel, three/four‐strands helical chains, and five‐strand helical chain with a single atom chain at the center of Si nanowires (NWs) inside single‐walled carbon nanotubes (Sin@SWCNTs) are obtained by means of molecular dynamics. On the basis of these optimized structures, the structural evolution of Sin@SWCNTs subjected to axial stress at low temperature is also investigated. Interestingly, the double parallel chains depart at the center and transform into two perpendicular parts, the helical shell transformed into chain, and the strand number of Si NWs increases during the stress load. Through analyzis of pair correlation function (PCF), the density of states (DOS), and the z‐axis polarized absorption spectra of Sin@SWCNTs, we find that the behavior of Sin@SWCNTs under stress strongly depends on SWCNTs' symmetry, diameter, as well as the shape of NWs, which provide valuable information for potential application in high pressure cases such as seabed cable. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
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A new pressure DSC module (Mettler DSC27HP) and its abilities for vapor pressure determination in the range of subambient
pressure to 7 MPa are presented. To compare the new to an established method, vapor pressures of caffeine, naphthalene and
o-phenacetin have been determined both by pressure DSC and the Knudsen effusion cell method. These results, including the
derived heats of evaporation and heats of sublimation, are compared to literature values.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The notions of internal pressure and its temperature coefficient are critically analyzed. The temperature coefficient of internal pressure is correlated with the peculiarities of supramolecular organization of liquid-phase systems. This relationship is characterized. 相似文献
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聚合物在高压下的结构、形态和性能(下)张雄伟,黄锐(成都科技大学塑料工程系,成都,610065)在上篇中我们介绍了结晶性聚合物在高压下结晶的结构和形态。本篇将介绍聚合物在高压下的结晶动力学和热力学以及聚合物在高压下的退火等方面内容。2高压结晶动力学研... 相似文献
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There is considerable interest in performing volatilisation and evaporation measurements by thermogravimetry. A quick and
simple method for determining vapour pressure using a conventional thermobalance and standard sample holders has been developed.
These yield meaningful thermodynamic parameters such as the enthalpies of sublimation and vaporisation. Under favourable conditions
the melting temperature and enthalpy of fusion of such compounds can be obtained. This technique has been used for the study
of dyes, UV absorbers and plasticisers. The use of modulated- temperature programs for such work is also described.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The combined effect of pressure and temperature on hydrophobic hydration of a nonpolar methanelike solute is investigated by extensive simulations in the TIP4P model of water. Using test-particle insertion techniques, free energies of hydration under a range of pressures from 1 to 3000 atm are computed at eight temperatures ranging from 278.15 to 368.15 K. Corresponding enthalpy, entropy, and heat capacity accompanying the hydration process are estimated from the temperature dependence of the free energies. Partial molar and excess volumes calculated using pressure derivatives of the simulated free energies are consistent with those determined by direct volume simulations; but direct volume determination offers more reliable estimates for compressibility. At 298.15 K, partial molar and excess isothermal compressibilities of methane are negative at 1 atm. Partial molar and excess adiabatic (isentropic) compressibilities are estimated to be also negative under the same conditions. But partial molar and excess isothermal compressibilities are positive at high pressures, with a crossover from negative to positive compressibility at approximately 100-1000 atm. This trend is consistent with experiments on aliphatic amino acids and pressure-unfolded states of proteins. For the range of pressures simulated, hydration heat capacity exhibits little pressure dependence, also in apparent agreement with experiment. When pressure is raised at constant room temperature, hydration free energy increases while its entropic component remains essentially constant. Thus, the increasing unfavorability of hydration under raised pressure is seen as largely an enthalpic effect. Ramifications of the findings of the authors for biopolymer conformational transitions are discussed. 相似文献
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《液相色谱法及相关技术杂志》2012,35(5):697-718
Abstract The investigation describes the HPLC separation of hydroxyl fatty acids as their methoxyphenacyl esters. All separations were performed using two types of reverse phase columns, μ-Bondapak C 18 and Fatty Acid Analysis columns. The solvent system consisted of acetonitrile: water gradient. A simple method for the trifluoroacetylation of the hydroxyl group is described which permits the identification of these specific fatty acids and decreases the lower limit in chain length determination for these fatty acids. A method for the hydrogenation of unsaturated fatty acid mixtures is described, and the effects of variations in time, temperature, pressure, and the amount of catalyst are examined on the percent hydrogenation of unsaturated to the saturated forms of the fatty acids. Further, the effects of the different variables are related to the percent of hydrogenation of the cyclopropane fatty acids. Evidence is provided on the hydrogenation of the cyclopropane which does not agree with previously described ring opening mechanisms which have been proposed from GLC data which may be due to the difference in temperatures under which the chromatographic processes are carried out. These findings indicated the possibility of isolating an intermediate in the process by HPLC. 相似文献
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The pressure dependence of the specific heat of poly(methyl methacrylate), polystyrene, and atactic and isotactic polypropylene was determined from simultaneous measurements of thermal conductivity and diffusivity in a cylindrical geometry at 300°K and in the pressure range 0–37 kbar. The thermal conductivity and the diffusivity both increase strongly with pressure, while the specific heat decreases. The pressure dependencies are most pronounced at low pressures. The results are compared with other experimental results and with theoretical calculations. 相似文献