化学平衡的图解

化学平衡常数的函数图示,简明地表示出在指定温度下体系所有可能的平衡状态,并能对反应体系的行为,譬如反应参与物的量的改变或气体压强的改变是否影响化学平衡,平衡移动的过程中体系组成所发生的一系列变化情况等,都能给予直观地说明。这种化学平衡的图解在教科书中还不多见,所见书中也只是讨论包含一种或两种可变浓度(或气体分压)的     

“化学平衡移动”的图示法

无机化学教科书对化学平衡的描述,常以一简图(见图1)表示:可逆反应的正反应速度V正随时间而减小,同时逆反应速度V逆随时间而增加,当V正=V逆时,体系处于平衡状态。此图简洁、直观、形象,学生容易接受。     

化学平衡移动图象判断几例

化学平衡移动常以图象表示,具有简明、直观、形象等特点,但这种图象是化学平衡中的难点之一,突破这一难点,是教好化学平衡移动的重要环节。     

高中生化学平衡迷思概念的调查研究

通过调查发现学生在学习化学平衡之后,仍然对化学平衡中的5大中心概念问题:(1)动态平衡的判断;(2)浓度、温度、压强(体积)等对化学平衡的影响;(3)浓度、温度、压强(体积)等对化学平衡反应速率的影响;(4)盐类对溶解平衡的影响;(5)惰性气体对化学平衡的影响等存在大量的迷思概念。在此基础上论文汇总了学生在化学平衡学习过程中存在的重要迷思概念以及对重要迷思概念产生原因进行了分析,最后得出结论,传统的教学很难转变学生的迷思概念。     

化学学历案促进深度学习的发生——化学平衡移动复习课

学历案是关于学习经历或过程的方案，利用学历案构建一个“以学为主、以教促学”的教学模式，改变了教师的主导地位，凸显了学生的主体地位。笔者尝试借助学历案，以花青素为载体，通过生活化的化学实验，将化学平衡常数K作为分析工具，进行证据推理，以外界条件使花青素溶液颜色变化，到花青素的工业合成为明线；以化学平衡移动的本质到化学平衡移动原理的应用为暗线，双线结合，学生自主建构“化学平衡移动”的认知模型，从而促进深度学习的发生。     

深入理解化学平衡常数及其应用——对2019年全国理综(Ⅰ卷)化学第28题的分析

在已有的化学平衡常数教学的基础上,提出认知化学平衡常数的新角度--化学平衡常数的多种表达式。依据教材中用浓度表示的化学平衡常数并结合理想气体状态方程,推导用物质的量分数及分压表示的化学平衡常数表达式,分析3者之间的区别和联系,进而应用化学平衡常数的多种表达形式解决2019年全国(Ⅰ卷)化学第28题中的相关问题,使学生深入理解解答这道高考试题的关键所在。同时,拓展了学生对平衡常数的认识,提升了学生灵活应用平衡常数解决问题的能力。     

有机物质的特殊磁性

一、引言大家知道,物质按其磁性通常可以分为逆磁体、顺磁体和铁磁体。逆磁体的磁化率是负值,数值通常在—13×10~(-6)至—0.8×10_(-6)的范围内,并且不依赖于温度和磁场强度。顺磁体的磁化率为正值,约在10~(-6)—10~(-3)数值范围内。磁化率大小反比于绝对温度,服从居里定律(x=1/(4KT)g~2β~2N),和磁场强度无关。铁磁体磁化率较大,其数值约在10~(-3)—10~3范围内,并和温度、磁场强度有关。铁磁体中有磁畴存在,居里点温度以上成为普通顺磁体。有机物质是共价键的化合物。而这些价键是由具有异向平行自旋的电子偶构成的,论其磁性应该是逆     

压强对化学平衡影响新实验方法探讨

高中课本“化学”关于压强对化学平衡影响的实验,是根据NO2和N2O4混合气体在加压(或减压)前后,气体颜色的变化来判断化学平衡移动方向的。     

二烷基二硫代磷酸锌的平衡解离及其与低氮分散剂的相互作用

本文用~(31)P-NMP研究了二烷基二硫代磷酸锌(ZDP)在内燃机基础油体系中的作用,发现在低浓度下从ZDP解离出一个含磷核的组份,化学位移为86ppm。表明ZDP在油中的溶解存在着依赖于浓度的化学平衡,通过这种平衡解离在ZDP与分散剂体系中的变化,研究了添加剂间的相互作用机理。     

化学平衡的多重性、稳定性和重现性

利用动力学方法讨论了非理想的化学反应体系中化学平衡态的多重性、稳定性和实验上的可重现性。分析了实验结果(化学平衡态)与初始条件以及其它动力学过程之间的依赖关系,并简略讨论了化学平衡多重性和稳定性问题在某些实际问题和工程设计中的重要性。     

Computational algorithms for matching polynomials of graphs from the characteristic polynomials of edge-weighted graphs

Computational algorithms are described which provide for constructing the set of associated edge-weighted directed graphs such that the average of the characteristic polynomials of the edge-weighted graphs gives the matching polynomial of the parent graph. The weights were chosen to be unities or purely imaginary numbers so that the adjacency matrix is hermitian. The computer code developed earlier by one of the authors (K.B.) is generalized for complex hermitian matrices. Applications to bridged and spirographs, some lattices and all polycyclic graphs containing up to four cycles are considered.     

Microscopic reversibility and reciprocal relations for Brownian molecular machines

Chemists have made great progress in synthesizing molecules that emulate in part the remarkable properties of biological molecular motors, most especially the ability to use chemical energy to drive directed motion and do mechanical work. Here the mechanism of a molecular motor is treated as a renewal process in which the motor molecule fluctuates away from, and then returns to some arbitrary initial configurational state. During this excursion, some number of fuel molecules will have been catalytically converted to product, and the motor will have undergone some number of mechanical cycles in which work is done on the environment. The dependences of the number of catalytic and mechanical processes per renewal obey reciprocal relations for arbitrarily strong load force and chemical driving force. These relations characterize the behavior of the system far from thermodynamic equilibrium in the same way that the Onsager reciprocal relations characterize the system close to thermodynamic equilibrium.     

Graphs and thermodynamics

Graphs are used in many fields of chemistry for codification and model purposes. One of these fields is widely known under the acronym QSAR/QSPR, i.e., quantitative structure–activity/structure–property relationships. In chemical graph studies directed graphs, known as digraphs, i.e., graphs with a preferred direction, have mainly been used to codify chemical reaction networks. Actually, digraphs, especially directed acyclic graphs together with simple graphs, can be used to draw a metalanguage of thermodynamics that codifies rules and properties which can be used to automatically derive many well-known, and less-known, thermodynamic relationships.     

DSC analysis of isothermal melt-crystallization, glass transition and melting behavior of poly(l-lactide) with different molecular weights

Isothermal melt-crystallization, glass transition and melting behavior of poly(l-lactide) (PLLA) with different molecular weights were investigated by using differential scanning calorimetry. Analysis by Avrami equation showed that crystallization was initiated by heterogeneous nucleation, followed by 3-dimensional growth. The maximum reciprocal half-time of crystallization (1/t_1/2) was detected at 105 °C. Double endothermic peaks were observed around the glass transition for PLLA with intermediate crystallinities, indicating the coexistence of bulk-like and confined amorphous regions. Double-melting behavior was analyzed and combined with the equilibrium melting temperature evaluation by non-linear Hoffman-Weeks extrapolation, from which a value of 207.6 °C was deduced for PLLA of infinite molecular weight. Lauritzen-Hoffman theory was employed to analyze the crystallization kinetics. Regime II-III transition was found to occur at 120 °C for PLLA of lower molecular weight. The crystal morphology was also examined by scanning electron microscopy through chemical etching method.     

A molecular model of water based on the lattice gas model

A lattice gas model is used to describe the vapor-liquid state of water molecules. The orientationally directed interaction of the water molecules via their tetrahedral structure and dipole-dipole interaction are considered in the theory, along with the Lennard-Jones contributions to the potential of molecular interaction, which stabilize the system with dipole interaction. We studied how the radius of the molecular interaction potential affects the equilibrium characteristics of the system (the phase separation curves of the vapor-liquid system, and the relationship between the fluid density and the chemical potential value).     

Phase separation behavior of aqueous solutions of a thermoresponsive polymer

Cloud‐point and binodal curves of the LCST type were obtained for aqueous solutions of a thermoresponsive polymer, poly [2‐(2‐ethoxy)ethoxyethyl vinyl ether], poly(EOEOVE). The cloud‐point curve obtained was very flat except in a dilute region, that is the cloud‐point temperature was insensitive to the polymer concentration, resembling the cloud‐point curve for aqueous solutions of poly(N‐isopropylacrylamide). On the other hand, the binodal curve obtained was parabolic, and located within the two‐phase region of the cloud‐point curve. Accompanied with the phase separation, a sharp endothermic peak was observed in a region including the cloud‐point and binodal temperatures. The reciprocal of the osmotic compressibility ?Π/?c obtained by sedimentation equilibrium indicated that water changes from a good to poor solvent for poly(EOEOVE) with increasing temperature. Analyzing the ?Π/?c data by a thermodynamic perturbation theory, we determined the interchain interaction parameters, the hard‐core diameter d and the depth ε of the square‐well potential. Theoretical binodal and endothermic curves calculated by the perturbation theory using the estimated interaction parameters reproduced experimental ones semiquantitatively, but the theoretical binodal disagreed with the experimental flat cloud‐point curve. The disagreement at high concentrations was in the opposite direction to that expected from the sample polydispersity in the molecular weight. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2937–2949, 2005     

Graph Theoretic Techniques in the Theory of Classical Fluids

Abstract

The mathematical ideas underlying the graph theoretic approach to the equilibrium theory of classical fluids are treated from an elementary point of view. The emphasis is placed on modern developments based on the techniques of functional differentiation and topological reduction. The aim is to provide the non-expert reader with a mathematical guide to recent papers which employ graph theoretic methods, particularly to those dealing with perturbation theory.     

Necessary and sufficient conditions for the appearance of extrema on concentration distribution curves in complex equilibrium systems

It is shown that species distribution curves with at least one minimum may be found in most equilibrium systems with three or more components. Whether such concentration minima are actually observed then depends on the values of the equilibrium constants and on the total (analytical) concentrations of the components. A general algorithm is given for the necessary and sufficient conditions for the appearance of extrema in multicomponent systems. Three-component systems are studied in more detail and special attention is given to the limiting case of a horizontal inflection, i.e., the point where the concentration minimum just disappears. Two well-studied chemical examples, the Cu(2+)-diethylenetriamine-OH(-) and Hg(2+)-Cl(-)-OH(-) systems are discussed, along with a simple model system showing as many as five extrema on a single distribution curve.     

Directed graphs of structurally stable potential energy surfaces representing a-priori reaction pathways

An intrinsic property of potential energy surfaces (PES) that holds within the adiabatic approximation is established: its structural stability.We derive the condition that ensures this property: There cannot be any integral curve of the gradient field of the PES that connects two classical transition state configurations without passing through another critical configuration in between.Under this situation, we can establish a one-to-one correspondence: a whole class of adiabatic PES defining one reaction mechanism is associated to a directed graph. Thus, the problem of finding a-priori pathways involving a given number m of chemical species narrows down to a classifying certain directed graphs with m sinks. The combinatorial method is derived in this paper.Detailed examples on a-priori pathways for degenerate thermal rearrangements and on 1-2 hydrocarbon shifts are worked out and found in agreement with experimental evidence.