稀溶液的渗透压、化学势、外压与蒸气压关系

以外压对化学势的影响为主线,从外压对化学势的改变和外压对稀溶液蒸气压的改变两个方面,讨论了稀溶液的渗透压、化学势、外压与蒸气压关系。以帮助学生更好地理解和掌握这些基本概念。     

热力学平衡中的假想态浅议

在热力学平衡中,假想态概念可拓展应用于稀溶液中溶质化学势等温式的推导、非均相体系中平衡常数的计算及电化学体系中电极电势的求算等。     

稀溶液中溶剂的化学势及其在依数性上的应用

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。     

微小液滴化学势及其在界面化学中的应用

推导了微小液滴化学势的关系式及其在界面化学中建立和推导相平衡关系的应用。     

利用前沿研究提高物理化学的教学效果

物理化学课程中抽象的概念、大量的公式以及结论的经典性容易给学生造成授课内容远离前沿研究的错觉。可以在授课过程中将前沿研究与课程内容相结合来改革物理化学教学。主要的实例包括：（1）利用△G判据分析利用水分解反应制取氢气的热力学要求;（2）利用离子互吸理论和双电层理论解释纳米孔的离子选择性;（3）基于化学势和电化学势的概念来推导浓差电池的电动势。通过揭示物理化学基本原理对上述前沿研究的指导作用来拓宽学生的视野,培养学生的学习兴趣,从而改善了课程的教学效果。     

簇合物(p-H2)N-HCCCN的结构和能量

采用两体作用势模型和遗传算法对簇合物(p-H2)NHCCCN的极小能量结构和能量进行了理论研究.结果表明,20个para-H2分子形成HCCCN周围的第一个溶剂层,第一个溶剂层包含三个溶剂环,每个溶剂环都有6个para-H2分子,第19和20个para-H2分子分别聚集在HCCCN分子的N、H原子末端.进一步计算了(p-H2)N-HCCCN的化学势,发现化学势随para-H2分子个数的增加呈震荡变化.     

簇合物(p-H2)N-HCCCN的结构和能量

采用两体作用势模型和遗传算法对簇合物(p-H2)N-HCCCN的极小能量结构和能量进行了理论研究.结果表明,20个para-H2分子形成HCCCN周围的第一个溶剂层,第一个溶剂层包含三个溶剂环,每个溶剂环都有6个para-H2分子,第19和20个para-H2分子分别聚集在HCCCN分子的N、H原子末端.进一步计算了(p-H2)N-HCCCN的化学势,发现化学势随para-H2分子个数的增加呈震荡变化.     

含Pb铝合金表面的电化学溶解趋势

利用一个简单层状模型通过第一性原理的密度泛函理论研究了表面Pb含量变化对Al(100)表面Al原子的化学势和电化学溶解电势的影响规律.计算结果表明,当表面层Pb含量为1/9、1/4、1/2和3/4 ML(monolayer)时,与纯铝相比,表面Al原子的化学势分别升高了0.13、0.17、0.57和0.64 eV,表面Al原子的溶解电极电势分别偏移了-0.04、-0.06、-0.19和-0.21 V.溶解电势向负方向偏移,表明含Pb的Al(100)表面的Al原子在更低的电势条件下就可以溶解了.同时,表面Pb含量不同会引起表面Al原子向内不同程度的弛豫,导致表面Al的化学环境和表面结构发生变化,进一步表明金属表面原子的化学势和溶解电极电势受原子周围的化学环境的影响.表面Mülliken电荷布居分析证实,随着表面Pb含量增加,Pb原子与Al原子之间的电荷交换作用增强,使表面Al原子总的负电荷数增加,导致表面电位下降,表面功函数也减小,也促使Al表面更易于发生电化学腐蚀反应.     

应用量子化学反应性指数评估化合物的亲核能力

评估化合物的亲核性能,对于设计化学反应的条件、研究反应机理、探讨药物与受体或酶作用靶点提供量子化学反应性参数,具有重要意义。本文在概念密度泛函理论的基础上,以得失电子前后化学势的变化,评估分子的反应性指数;用福井函数值,计算分子中各原子的反应性指数。选择脂肪胺、氨基酸和芳香胺三类胺及常用阴离子为研究对象,采用Gaussian软件分别对化合物分子及其失电子态进行结构优化和单点能计算。结果显示,建立的化学势变化值作为反应性指数的评估方法,与实验值基本吻合;所研究的几种有机分子的福井函数值与实际亲核能力基本一致。这表明可以采用得失电子前后的化学势变化值和福井函数值来预测分子和原子的亲核反应性。     

流体熵相关性质的Monte Carlo模拟新方法

提出了用于计算实际体系熵相关性质的Monte Carlo 多级取样分子模拟方法.应用这一方法,对硬球流体的化学势及Helmholtz 自由能进行了估算,得到了满意的结果.计算化学势时,不存在通常试验粒子方法所遇到的高密度问题.该方法特别适合规律性的系统研究,较之普通模拟方法要有效得多.模拟得到的硬球体系无限稀释组份的超额化学势与对比直径的关系,在相变区域为一条双凹曲线;无论是在相变区还是在单相区,Carnahan-Starling 公式对这一关系的描述均有较大偏差.     

液化石油气自然气化钢瓶中组分变化的模拟计算

根据化学相平衡原理、质量守恒定律和实际气体状态方程，建立了液化石油气自然气化过程气相和液相组分变化理论计算的模型，可对多组元LPG自然气化过程中各组分的变化进行准确的计算，同时可计算组分变化引起饱和蒸气压、热值、华白数和燃烧势的变化。     

Thermodynamics and partitioning of homopolymers into a slit-A grand canonical Monte Carlo simulation study

Grand canonical ensemble Monte Carlo simulation (GCMC) combined with the histogram reweighting technique was used to study the thermodynamic equilibrium of a homopolymer solution between a bulk and a slit pore. GCMC gives the partition coefficients that agree with those from canonical ensemble Monte Carlo simulations in a twin box, and it also gives results that are not accessible through the regular canonical ensemble simulation such as the osmotic pressure of the solution. In a bulk polymer solution, the calculated osmotic pressure agrees very well with the scaling theory predictions both for the athermal polymer solution and the theta solution. However, one cannot obtain the osmotic pressure of the confined solution in the same way since the osmotic pressure of the confined solution is anisotropic. The chemical potentials in GCMC simulations were found to differ by a translational term from the chemical potentials obtained from canonical ensemble Monte Carlo simulations with the chain insertion method. This confirms the equilibrium condition of a polymer solution partition between the bulk and a slit pore: the chemical potentials of the polymer chain including the translational term are equal at equilibrium. The histogram reweighting method enables us to obtain the partition coefficients in the whole range of concentrations based on a limited set of simulations. Those predicted bulk-pore partition coefficient data enable us to perform further theoretical analysis. Scaling predictions of the partition coefficient at different regimes were given and were confirmed by the simulation data.     

A differential approach to calculating osmotic equilibrium for multisolvent systems

A differential approach to the calculation of osmotic pressure of multisolvent systems within the Lewis–Randall framework is presented in this paper. Exact differential equations relating the osmotic pressure and the system composition along paths of constant solvent chemical potential are obtained and numerically solved. Although even for the simple case of an ideal solution no analytic expression for the osmotic pressure can be obtained, the system of differential equations does not pose numerical difficulties to be solved. Examples of the use of the proposed methodology are presented using the two-suffix Margules and Flory–Huggins equations, allowing an assessment of the influence of liquid-phase non-ideality on the performance of the method, and showing that it can be applied even for systems wherein liquid–liquid phase equilibrium occurs.     

Lennard-Jones流体气液相图的粒子交换分子动力学模拟研究

利用粒子交换分子动力学模拟方法(Particle exchange molecular dynamics,PEMD)研究了Lennard-Jones流体的气液相图．模拟中,用两个耦合箱分别代表液相和气相．通过直接比较两箱的粒子化学势来控制交换粒子,从而达到两相平衡．采用Widom方法计算化学势．两模拟箱平衡时具有相同的温度、压强和粒子化学势．模拟的气液相图结果与利用其它方法得到的Lennard-Jones流体气液相图符合得很好．     

Influence of flow parameters of the mobile phase on the retention and thermodynamic characteristics of sorption in gas-liquid chromatography

The influence of the flow parameters of the mobile phase (flow rate and mean pressure in the column) on the retention and thermodynamic characteristics of sorption in gas-liquid chromatography is studied experimentally. Conditions are formulated under which the chromatographic process can be described in terms of the theory of equilibrium gas-liquid chromatography with an ideal gas as the mobile phase and the distribution of the sorbate between phases is not affected by the presence of a weakly sorbed carrier gas.     

Measurement of the Solubility of Volatile Substances by Vapor-Phase Gas-Chromatographic Analysis

A new procedure is proposed for vapor-phase gas-chromatographic determination of the solubilityof partly soluble volatile compounds in liquids. The method is based on successive pneumatic sampling totake small, equal portions of the equilibrium gas from the gas-liquid system containing an excess ofthe volatile component forming the second liquid phase. The gas-chromatographic determination of thiscomponent in the samples of the equilibrium gas makes it possible to find the slope of the isotherm describing the distribution of the substance between the liquid and gas phases near the saturation point, estimate the nonlinear portion of the isotherm, and calculate the substance content in the saturated solution.     

Osmotic Pressure and Phase Boundary Determination of Multiphase Systems by Analytical Ultracentrifugation

We show that analytical ultracentrifugation can be applied to derive full equations of state of colloids in a single sedimentation equilibrium experiment, by determination of single‐phase boundaries as well as of osmotic pressure versus concentration at fixed temperatures. A continuous dependence of the osmotic pressure, over orders of magnitude between at least ～10¹ and 10⁴ Pa, and a wide concentration range, are determined in agreement with standard theoretical considerations. Two model experimental colloidal systems are investigated: For a well‐known synthetic clay system (laponite), it is shown that two regimes—counter‐ion ideal gas and interacting double layers—can easily be identified in the equation of state, whereas metastable glass‐ or microphase‐separated gel states previously encountered in osmotic stress measurements of laponite are circumvented. For the case of rigid, crystallized catanionic bilayers, single phase domains can be identified. Osmotic pressure results in this case disagree with results obtained using the classical osmotic stress technique, as a result of sample adhesion to the ultracentrifuge cell windows and uncertainty due to possible micromolar ion contamination.     

Determination of gas-liquid partition coefficients by automatic equilibrium headspace-gas chromatography utilizing the phase ratio variation method

Summary The new phase ratio variation method is described which represents a convenient way for the determination of gas-liquid partition coefficients for practical purposes, utilizing equilibrium headspace-gas chromatography (EHS-GC). This method is based on the relationship between reciprocal peak area and the phase ratio in the vial containing the sample solution; it involves regression analysis of the EHS-GC measurements of a number of sample vials containing the same sample solution but with a wide variation of phase ratios. Examples are given for both aqueous systems and systems consisting of a stationary (liquid) phase used as the solvent; comparison of the measured values with results obtained by other methods shows satisfactory agreement. A critical discussion of the conditions influencing the accuracy of the analytical results is given.Symbols which specifically refer to gas chromatography (GC), to equilibrium headspace sampling (EHS) and to EHS-GC are marked by the corresponding acronym.     

The "Le Chatelier's principle"-governed response of actin filaments to osmotic stress

Actin filaments inhibit osmotic stress-driven water flow across a semipermeable membrane in proportion to the filament concentration (Ito, T.; Zaner, K. S.; Stossel, T. P. Biophys. J. 1987, 51, 745). When the filaments are cross-linked by F-actin binding protein, filamin A, this flow is stopped completely (Ito, T.; Suzuki, A.; Stossel, T. P. Biophys. J. 1992, 61, 1301). No conventional theory accurately accounts for these results. Here, this response is analyzed by formulating the entropy of the system under osmotic stress. Results demonstrate that the response of the actin filaments to osmotic stress is governed by the Le Chatelier's principle, which states that an external interaction that disturbs the equilibrium brings about processes in the body that tend to reduce the effects of this interaction. In the present case, disrupting equilibrium by osmotic stress brings about a reaction that decreases the chemical potential of water in the F-actin solution, reducing the effect of the applied osmotic disturbance. This decrease in the chemical potential of the water in the F-actin solution is caused by an increase in the chemical potential of F-actin, which is induced by isothermal absorption of heat by F-actin aided by work done by osmotic stress. As a result, F-actin has an inhibitory effect on the osmotic stress-driven water flow, and can even completely stop the flow when it is cross-linked. This is the first report demonstrating that the Le Chatelier's principle applies to the reaction of biopolymers against equilibrium disturbances such as osmotic stress.     

Analysis of osmotic pressure data for aqueous protein solutions via a multicomponent model

Integral equation theories and Monte Carlo simulations were used to study the Donnan equilibrium, which is established by an equilibrium distribution of a simple electrolyte between an aqueous protein-electrolyte mixture and an aqueous solution of the same simple electrolyte, when these two phases are separated by a semipermeable membrane. In order to describe the unusually low osmotic pressure found in many experiments we assumed that protein molecules can form dimers. The model solution contains proteins in a monomeric form, represented as charged hard spheres, or in a dimerized form, modeled as fused charged hard spheres. The counterions and coions were also modeled as charged hard spheres but of a much smaller size. The associative mean spherical and hypernetted-chain approximations were applied to this model. In addition, Monte Carlo computer simulations were performed for the same model system mimicking a lysozyme solution in the presence of 0.1 M sodium chloride. Theory and simulations were found to be in reasonably good agreement for the thermodynamic properties such as chemical potential and osmotic pressure under these conditions. Using the theoretical approaches mentioned above, we analyzed the experimental data for the osmotic pressure of bovine serum albumin in 0.15 M sodium chloride, human serum albumin solution (HSA) in 0.1 M phosphate buffer, and lysozyme in sulphate and phosphate buffers. The theoretically determined osmotic coefficients were fitted to the existing experimental data in order to obtain the fraction of dimers in solution. Our analysis indicated that there was relatively small self-association of protein molecules for bovine serum albumin solutions at pH=5.4 and 7.3, with the fraction of dimers smaller than 10%, while at pH=4.5 the dimer fraction was equal to 50%. In the case of HSA solutions, strong negative deviations from the ideal value were found and at pH=8.0 a reasonably good agreement between the theory and experiment is obtained by assuming full dimerization. For HSA solution at pH=5.4, the best fit to the experimental results was obtained for a fraction of dimers equal to 80%.