化学平衡的本质——浅谈混合熵对化学平衡的贡献

化学平衡是物理化学的重要内容之一。化学反应的等温方程式,给出了平衡常数与标准摩尔反应Gibbs自由能的关系。然而,仅从化学反应等温方程式还很难理解混合熵对化学平衡贡献的本质。本文建立了理想气体体系Gibbs自由能与反应进度的关系,给出了三个理想气体反应体系Gibbs自由能与反应进度的具体关系,分析了混合熵对化学平衡的本质贡献。     

Study on conductance of supersaturated chloride microdroplets

By using the measuring system previously designed by the authors, the conductance of KCl, NaCl and NH₄Cl microdroplets is obtained in the whole measuring RH range, especially in the supersaturation region, which cannot be acquired from the bulk solutions and fills the gap of lack of experimental data of conductance under the supersaturated state. The ERH and DRH of these three kinds of microdroplets observed from a microscope are 80.5% and 95.4% (KCl), 75.7% and 93.3% (NaCl), and 69.9% and 96.6% (NH₄Cl), respectively. In addition, it can be found from the dependence of conductance on RH that conductance is very sensitive to the existence of water molecules inside the microdroplet and the threshold of the deliquescence process can be predicted by the variation of conductance. Supported by the National Natural Science Foundation of China (Grant Nos. 20673010 and 20605004), Fundamental Research Foundation of BIT (Grant No. 20060742003), Program of Introducing Talents of Discipline to Universities (Grant No. B07012), and China Postdoctoral Science Foundation (Grant No. 20070410467)     

原位化学沉积法制备碳/聚苯胺复合材料作为超级电容器材料的研究

Polyaniline （PA） film was chemically deposited onto the surface of activated carbon （AC） uniformly. Chemical deposition was carried out in 0.1 mol/L aniline plus 0.5 mol/L H2SO4 solution adopting V2O5·nH2O coated on the surface of activated carbon as oxidant. The surface morphologies and structures of the composite materials were characterized by scanning electron microscopy and FT-IR spectra. The electrochemical properties of the composite material electrodes were studied by cyclic voltammetry and constant current charge/discharge tests in 1 molFL H2SO4 solutions. The specific capacitance of composite materials was exhibited as high as 237.5 F/g at a current density of 1.0 A/g compared with a value of 120 F/g for pure carbon electrode. Good power characteristic and good stability of composite electrodes were also demonstrated.     

FTIR-ATR <Emphasis Type="Italic">in situ</Emphasis> observation on the efflorescence and deliquescence processes of Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> aerosols

The efflorescence and deliquescence processes of Mg(NO₃)₂ aerosol particles deposited on ZnSe substrate have been investigated through in situ Fourier transform infrared-attenuated total reflection (FTIR-ATR) technique at the molecular level. At relative humidity (RH) of ∼3%, Mg(NO₃)₂ particles existed as amorphous states. The amorphous Mg(NO₃)₂ particles were transformed into crystalline Mg(NO₃)₂ · nH₂O (n ≤ 5) with slight increasing of RH. Thermodynamically stable Mg(NO₃)₂·6H₂O crystals were gradually formed on the particle surface and started to be dissolved at the saturation point (∼53% RH). At the same time, a continuous phase transition from Mg(NO₃)₂ · nH₂O (n≤5) to Mg(NO₃)₂·6H₂O occurred on the particle surface. This led the solid particles to completely deliquesce at 76% RH, which was much higher than the saturation point of 53% RH. In the efflorescence process, Mg(NO₃)₂ droplets entered into the supersaturated region due to the gradual evaporation of water. Finally, amorphous particles were formed when RH decreased below 5%. In the FTIR-ATR spectra of the supersaturated Mg(NO₃)₂ droplets, the absorbance of the symmetric stretching vibration of NO ₃ ⁻ (v ₁- NO ₃ ⁻ ) clearly became stronger. It resulted from the continuous formation of solvent share ion pairs (SIPs), and even the contact ion pairs (CIPs) between Mg²⁺ and NO ₃ ⁻ . Supported by the Trans-Century Program Foundation for the Talents by the Ministry of Education of China, the National Natural Science Foundation of China (Grant Nos. 20073004, 20473012, and 20673010), the 111 Project (B07012), and the State Key Laboratory of Physical Chemistry for Solid Surface of Xiamen University     

Measurement of the association constants through micro-Raman spectra of supersaturated lithium perchlorate droplets

High quality micro-Raman spectra of the LiClO4droplet with mass of nanogram scale were obtained at various concentrations from dilute to supersaturated state.From component band analysis of the v1-ClO4band,four peaks at 933.3,936.8,942.1 and950.7 cm 1were identified and assigned to free solvated perchlorate anion,solvent-shared ion pair,contact ion pair and complex ion aggregates,respectively.As expected,the signature of free solvated ClO4ion was observed to decrease in intensity with the increase in concentration.The intensity of the signature from solvent-shared ion pair was observed to rise with increase in concentration from 1.8 mol/kg to 5.0 mol/kg before decreasing as the concentration was further increased to 5.6mol/kg.Signatures of contact ion pair and of complex ion aggregates were shown to increase as the concentration was enhanced.Based upon the Eigen mechanism,we show that three association equilibria can be used to describe the transformations between free solvated perchlorate anion,solvent-shared ion pair,contact ion pair and complex ion aggregates.The overall association constant,K,and the stepwise association constants Ki(i=1 to 3)in the Eigen mechanism were determined separately with values of 0.025±0.003,0.023±0.002,0.068±0.033 and 0.686±0.174.Based on these constants,the electronic performance can be reasonably predicted by the optimum choice of electrolyte concentrations.     

活塞圆筒容器中铁磁居里温度的一种测量方法

 本文介绍了在活塞-圆筒型装置中建立的高压下原位测量居里温度的方法。采用简单的测量电路，不需要锁相放大器等精密仪器，系统仍具有较高的灵敏度，足以满足测量小样品的要求。合理的高压组装结构保证了测量的成功率。实验结果表明，测量的重复性误差小于±1 ℃。