Chemical oscillations

A chemical reaction is usually thought of as coming together of reactant molecules to form products. The concentrations of initial components (reactants) decrease, and concentrations of products increase until they reach a well defined state: the equilibrium. This process is accompanied by a decrease of the system free energy (compared at constant pressure and temperature), until it reaches a minimum in the equilibrium. Thus, it follows from the nature of the law of mass-action that every simple reaction approaches its equilibrium asymptotically, and the evolution of any physico-chemical system leads invariably to the steady state of maximum disorder in the universe. Normally, chemical systems approach equilibrium in a smooth, frequently exponential relaxation. Under special circumstances, however, coherent behavior such as sustained oscillations are observed and the oscillations of chemical origin have been present as long as life itself. Such reactions can be studied using mathematical models, the Lotka-Volterra model being the earliest and the simplest one.     

The Kinetic-Molecular and Thermodynamic Approaches to Osmotic Pressure: A Study of Dispute in Physical Chemistry and the Implications for Chemistry Education

Osmotic pressure proves to be a useful topic for illustrating the disputes brought to bear on the chemistry profession when mathematics was introduced into its discipline. Some chemists of the late 19th century thought that the introduction of mathematics would destroy that chemical feeling or experience so necessary to the practice of chemistry. These chemists were critical of the suggestion that mathematically analogous expressions for macroscopic phenomena implied similar kinetic-molecular processes at the microscopic level because they believed that a chemical phenomenon discovered by chemical experience through experiment was a more reliable guide to molecular processes than was mathematics. In general physical chemists of the modern era are also critical of the suggestion that mathematically analogous expressions for macroscopic phenomena imply similar kinetic-molecular processes at the microscopic level but for different reasons. The mathematical analogy between the van’t Hoff law and the ideal gas law is regarded as an artefact of the mathematical thermodynamic treatment of osmosis and not as a result of a correlation of kinetic-molecular processes. Some chemists however, albeit a minority, while agreeing with the thermodynamic treatment of osmotic pressure suggest that the mathematical analogy is more significant than being simply a mathematical artefact. They propose a controversial kinetic-molecular model of osmotic pressure which they believe has more educational value than the thermodynamic model. The significance of mathematically analogous expressions for different chemical properties and the desirability of highlighting unifying chemical principles for the teaching and learning of tertiary level chemistry are discussed predominantly in the context of historical osmotic studies.     

From Chemical Forces to Chemical Rates: A Historical/Philosophical Foundation for the Teaching of Chemical Equilibrium

With this paper, our main aim is to contribute to the realisation of the chemical reactivity concept, tracing the historical evolution of the concept of chemical affinity that eventually supported the concept of chemical equilibrium. We will concentrate on searching for the theoretical grounds of three key chemical equilibrium ideas: ?incomplete reaction’, ?reversibility’ and ?dynamics’. In addition, the paper aims to promote teachers’ philosophical/historical chemical knowledge. The starting point of this historical reconstruction will be the state of the art in the construction of the first affinity tables, based on the concept of elective affinities, during the 18th century. Berthollet reworked this idea, considering that the amount of the substances involved in a reaction was a key factor accounting for the chemical forces. Guldberg and Waage attempted to measure those forces, formulating the first affinity mathematical equations. Afterwards, the first ideas providing a molecular interpretation of the macroscopic properties of equilibrium reactions are presented. Eventually, theoretical chemists integrated previous findings into a new field: thermodynamics. This historical approach may serve as a base for an appropriate sequencing of the teaching and learning of chemical equilibrium. Hence, this paper tries to go beyond the simple development of teachers’ conceptions of the nature of chemistry, for it gives suggestions about how teachers may translate such understandings into classroom practice.     

Organic synthesis using clay catalysts

Conclusion The clay minerals can catalyze a variety of organic reactions occurring on their surface and interstitial space. Synthetic organic chemists have been attracted to their tremendous potential as catalysts only relatively recently. Modification of their properties by incorporating different metal cations, molecules or complexes, can lead to catalysts that are useful in effecting even more varieties of reactions and higher selectivity in product structure and yield. There is a theory that the molecules of life actually developed in sedimentary clays. As the organic chemist is becoming more aware of the clay’s efficacy, its uses in organic synthesis are bound to increase, especially because it helps in developing eco-friendly chemical processes. The dark clay has a bright future in the area of organic synthesis.     

用于抑制区域间振荡的新型FACTS装置(英文)

随着大系统的互联,出现了区域间振荡现象．为抑制这种振荡,本文提出了一种新的ＦＡＣＴＳ装置,并根据输电线模型和纵向机电模型的相似性,推导了该ＦＡＣＴＳ装置的最佳参数和最佳安装位置的确定方法．用一４２０ｋＶ 纵向系统和一个复杂电力系统为例进行了仿真计算．结果显示该装置可有效地抑制区域间振荡．     

Chemistry at the Nanoscale

Traditionally the kinetics of a chemical reaction has been studied as a set of coupled ordinary differential equations. The law of mass action, a tried and tested principle for reactions involving macroscopic quantities of reactants, gives rise to deterministic equations in which the variables are species concentrations. In recent years, though, as smaller and smaller systems – such as an individual biological cell, say – can be studied quantitatively, the importance of molecular discreteness in chemical reactions has increasingly been realized. This is particularly true when the system is far from the ‘thermodynamic limit’ when the numbers of all reacting molecular species involved are several orders of magnitude smaller than Avogadro’s number. In such situations, each reaction has to be treated as a probabilistic ‘event’ that occurs by chance when the appropriate reactants collide. Explicitly accounting for such processes has led to the development of sophisticated statistical methods for simulation of chemical reactions, particularly those occurring at the cellular and sub-cellular level. In this article, we describe this approach, the so-called stochastic simulation algorithm, and discuss applications to study the dynamics of model regulatory networks.     

The Roles of Representations and Tools in the Chemistry Laboratory and Their Implications for Chemistry Learning

In this historical and observational study, we describe how scientists use representations and tools in the chemistry laboratory, and we derive implications from these findings for the design of educational environments. In our observations we found that chemists use representations and tools to mediate between the physical substances that they study and the aperceptual chemical entities and processes that underlie and account for the material qualities of these physical substances. There are 2 important, interrelated aspects of this mediational process: the material and the social. The 1st emphasizes the surface features of both physical phenomena and symbolic representations, features that can be perceived and manipulated. The 2nd underscores the inherently semiotic, rhetorical process whereby chemists claim that representations stand for unseen entities and processes. In elaborating on our analyses, we ? Examine the historical origins and contemporary practices of representation use in one particular domain-chemistry-to look at how developments in the design of representations advance the development of a scientific community, as well as the understanding of scientists engaged in laboratory practice. ? Examine representations spontaneously generated by chemists, as well as those generated by their tools or instruments, and look at how scientists-individually and collaboratively-coordinate these 2 types of representations with the material substances of their investigations to understand the structures and processes that underlie them. ? Draw implications from the study of scientists to make recommendations for the design of learning environments and symbol systems that can support the use of representations by students to understand the structures and processes that underlie their scientific investigations and to engage them in the practices of knowledge-building communities.     

Scaffolding Students’ Online Critiquing of Expert- and Peer-generated Molecular Models of Chemical Reactions

In this study, we developed online critiquing activities using an open-source computer learning environment. We investigated how well the activities scaffolded students to critique molecular models of chemical reactions made by scientists, peers, and a fictitious peer, and whether the activities enhanced the students' understanding of science models and chemical reactions. The activities were implemented in an eighth-grade class with 28 students in a public junior high school in southern Taiwan. The study employed mixed research methods. Data collected included pre- and post-instructional assessments, post-instructional interviews, and students' electronic written responses and oral discussions during the critiquing activities. The results indicated that these activities guided the students to produce overall quality critiques. Also, the students developed a more sophisticated understanding of chemical reactions and scientific models as a result of the intervention. Design considerations for effective model critiquing activities are discussed based on observational results, including the use of peer-generated artefacts for critiquing to promote motivation and collaboration, coupled with critiques of scientific models to enhance students' epistemological understanding of model purpose and communication.     

Optimization of a Reduced Chemical Kinetic Model for HCCI Engine Simulations by Micro-Genetic Algorithm

A reduced chemical kinetic model （44 species and 72 reactions） for the homogeneous charge compression ignition （HCCI） combustion of n-heptane was optimized to improve its autoignition predictions under different engine operating conditions. The seven kinetic parameters of the optimized model were determined by using the combination of a micro-genetic algorithm optimization methodology and the SENKIN program of CHEMKIN chemical kinetics software package. The optimization was performed within the range of equivalence ratios 0.2-1.2, initial temperature 310- 375 K and initial pressure 0, 1-0.3 MPa, The engine simulations show that the optimized model agrees better with the detailed chemical kinetic model （544 species and 2 446 reactions） than the original model does.     

化学污染物处理方法

化学实验室是一个较为严重的污染源,合理遏制或减轻化学实验室的污染是化学工作者的责任。分析了目前实验室存在的污染种类及危害,并针对不同污染提出相应治理办法,对本校实验室污染防治措施提出改进意见。     

Fascinating organic molecules from nature

From the very beginning of civilization, humans have used chemicals from Nature ?? most of them comparatively small organic molecules now designated as secondary metabolites ?? for a variety of purposes such as pigments and dyes, arrow and fish poisons and olfactory stimulants. It is no wonder that many eminent chemists were attracted to these materials to elucidate the underlying chemistry. Willstatter, Baeyer, Richard Kuhn, Karrer, Robinson and others made pioneering studies and isolated several new compounds which were included in the curriculum of earlier days. Another pioneer, A G Perkin, second son of Sir W H Perkin, was, according to his elder brother, W H Perkin, Jr, a dabhand with natural dyes.He andAE Everest wrote a book The Natural Organic Colouring Matters, first published in 1918, which was like a Bible to natural product chemists of yesteryears. (You can now read it on line!). As organic chemistry progressed, making leaps and bounds, the newer exciting discoveries gradually pushed the study of several of these compounds out of the curriculum. While one can understand this trend, one also feels sad that students these days are not aware of several interesting facets of natural products chemistry which link organic chemistry with folklore, traditional practices by diverse native communities, indigenous systems of medicine and current ideas of chemical structure and reactivities. It is not possible to fill in these gaps in textbooks which are designed to cater to the needs of students preparing for various university examinations, but articles such as those contemplated here can provide students with knowledge that can be stimulating, interesting as well as enjoyable! We begin the series with ??some exotic red pigments of plant origin??. Several red coloured dyes and pigments of vegetable origin have been known to mankind ever since the dawn of civilization. Their varied uses have been mentioned in ancient literature, including the Ramayana, folklores, travelogues and accounts of several explorers. Their chemistry is equally fascinating and has attracted the attention of a number of eminent organic chemists. In this article, we examine a few of these pigments isolated from plant materials found in different parts of the world. They include the pigments of the red sandalwood, the colourants of safflower, the exotic cosmetic chica red, brazilin from the Brazil wood (and the related hematoxylin), the compounds from the Dragon??s blood, the sesquiterpene quinones of the Miro wood and rottlerin, the main red pigment of Kamala dye.     

2016 Nobel Prize in Chemistry

The Nobel Prize in Chemistry for the year 2016 was awarded to three illustrious chemists, Professors Jean-Pierre Sauvage, Sir Fraser Stoddart, and Ben Feringa. Pioneering works of these chemists on designing molecules, chemically synthesizing them, and extracting a work out of such designed molecules open-up a new area of chemistry in a paradigm shifting manner. Beginning with controlling the molecular motions, particularly involving interlocked macrocycles in late 1980s, the advancement progressed to envelop energy storage and retrieval, and varieties of examples around the concept. Molecular motion alone can also be a rich source for such a work output has also been established. These developments possess the required momentum to uncover a new area of chemistry, wherein energy input-output can be used beneficially to conduct a useful work, in a close analogy to machines such as an electric motor.     

Students’ Ideas about How and Why Chemical Reactions Happen: Mapping the conceptual landscape

Research in science education has revealed that many students struggle to understand chemical reactions. Improving teaching and learning about chemical processes demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the domain. Thus, we have carried out a qualitative study to explore students reasoning about chemical causality and mechanism. Study participants included individuals at different educational levels, from college to graduate school. We identified diverse conceptual modes expressed by students when engaged in the analysis of different types of reactions. Main findings indicate that student reasoning about chemical reactions is influenced by the nature of the process. More advanced students tended to express conceptual modes that were more normative and had more explanatory power, but major conceptual difficulties persisted in their reasoning. The results of our study are relevant to educators interested in conceptual development, learning progressions, and assessment.     

Administrative service and research performance: A study of chemistry department heads

This study explores the effect of administrative service as department chair on the scholarly careers of academic chemists through an analysis of their publication and doctoral student productivity records over a two-decade period. A longitudinal experimental design is employed with a control group of academic chemists who have not served in an administrative capacity throughout the equivalent time period. The results of the study indicate no significant difference in the publication and doctoral student productivity levels of the experimental and control groups. These results suggest that universities have been successful in attracting and retaining the services of productive scholars as department heads and that such service does not diminish their long-term scholarly productivity.Presented at the 24th Annual Forum of the Association for Institutional Research, Fort Worth, Tex., May 1984.     

The Lens of Chemistry

Chemistry possesses a distinctive theoretical lens—a distinctive set of theoretical concerns regarding the dynamics and transformations of a perplexing variety of organic and nonorganic substances—to which it must be faithful. Even if it is true that chemical facts bear a special (reductive) relationship to physical facts, nonetheless it will always still be true that the theoretical lenses of the two disciplines are distinct. This has consequences for how chemists pursue their research, as well as how chemistry should be taught.     

Students' conceptions of chemical change

One hundred high school chemistry students who had completed a unit on chemical change were given a written instrument in which they were shown three oxidation-reduction reactions and were asked to explain them. Eleven students representing a range of achievement levels were chosen for more intensive clinical interviews in which they explained their responses, evaluated the quality of their responses, and compared them to other hypothetical responses. Interview results revealed that students commonly experienced difficulties at three different epistemological levels: 1. Chemical knowledge. Most students failed to invoke atoms and molecules as explanatory constructs, even though they had been emphasized in their chemistry course. Some students also listed “substances” such as heat, cold, or decay as reactants or products. 2. Conservation reasoning. Many students could not predict or explain mass changes in the chemical reactions. Their most common problems included (a) a tendency to treat chemical changes such as rusting as physical changes in form or state, and (b) failure to understand the role of invisible (in this case gaseous) reactants or products in the reactions. 3. Explanatory ideals. Many students demonstrated a preference for explanations based on superficial analogies with everyday events (e.g., rusting is like decay) over explanations based on chemical theories. Only one of the 11 students interviewed demonstrated mastery of the unit's contents at all three levels. Results of this and other research indicate a need for substantial revision in chemistry teaching practice.     

Mastery,insight, and the teaching of chemistry

The learning of chemistry is described as a process analogous to the process of making chemical discoveries. Historical examples are given to show how chemists have used their insight to break out of a conceptual loop in order to advance the science. Having the insight to make the intuitive leap necessary to break a conceptual loop is as important as having the mastery of the pertinent facts. As in making chemical discoveries, learning elementary chemistry requires developing insight as well as acquiring mastery of the facts. However, current general chemistry teaching tends to teach facts first and insight later. Suggestions for improving this situation so that insight and facts are learned together are given. Finally, the nature of insight is probed more deeply and presented as a two-step process where the first step is an evaluation of the perceptions about science which are held. Once the student, teacher, or researcher has a clear evaluation of the validity of the perceptions that he or she holds, further significant progress toward understanding or scientific discovery is possible.     

The History of Chemistry. The Case of the Supposed Isomerism of the Hydrocarbon Ethane in the Construction of Knowledge: Implications for chemical education

We contend that Chemical education proposals for changing the conception of chemistry literacy should include making explicit the relationship between chemistry as science and chemistry as technology. The potential for increasing students' confusion about what these interconnected activities involve is significant. In this paper we illustrate the importance of distinguishing between scientific and technological activities by explaining the events and processes that are occurring, firstly between material objects (instruments, machines) and practical activities and ideas; and secondly between ideas (theory) which may be called explanations and those that we call knowhow. We illustrate this by exploring the controversy in the development of chemical theory in history - the supposed isomerism of ethane. The additional purpose of this article is to highlight the importance of the history of chemistry in the education of chemists.     

提高环境保护意识,建立绿色化学实验室

高等学校的化学实验容易造成对环境的污染，建立无污染的绿色化学实验事不仅是化学工作荇自身的需要，也是埘社会的负责，是培养学生牢牢树立保护环境意识的有效措施。该文介绍南京大学国家级化学实验教学示范中心采取多方面的有效措施减少化学实验对环境的污染和建立绿色化学实验室的措施。