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A transição progressiva dos modelos de ensino sobre cinética química a partir do desenvolvimento histórico do tema; Progressive transitions in models on chemical kinetics from the historical development of the subject

Martorano, Simone Alves de Assis
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 25/10/2012 PT
Relevância na Pesquisa
66.27%
Atualmente, no ensino médio brasileiro, o tema cinética química tem sido apontado por professores do ensino médio como sendo de difícil abordagem devido ao caráter empírico como também abstrato dos conhecimentos envolvidos. Levando em consideração essas dificuldades, o objetivo desta pesquisa foi o de identificar como uma abordagem com foco na história da ciência pode contribuir para uma transição progressiva de professores de química do ensino médio no que se refere ao modelo de ensino de cinética química, considerando os conteúdos e as estratégias de ensino utilizadas. Para alcançar esse objetivo foi oferecido um curso de formação continuada para 20 professores de química, em que foi apresentado o tema cinética química na perspectiva do desenvolvimento histórico desse tema (reconstrução histórica), permitindo assim uma melhor compreensão do contexto no qual esses conceitos foram desenvolvidos. Baseando-se na perspectiva de Lakatos, foram construídos modelos de ensino de cinética química a partir das ideias dos professores, procurando-se verificar se esses modelos formam sequências de transição progressiva, similares ao que Lakatos, na História da Ciência, se refere a "problemática" que aumenta o poder explanatório/heurístico do modelo. A evolução dos modelos...

As concepções de ciência dos livros didáticos de química, dirigidos ao ensino médio, no tratamento da cinética química no período de 1929 a 2004; The science conceptions of chemical textbooks addressed to the high school, in treatment of chemical kinetics during the period from 1929 to 2004

Martorano, Simone Alves de Assis
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/04/2007 PT
Relevância na Pesquisa
66.27%
O objetivo central deste trabalho foi investigar como a Cinética Química foi sendo apropriada pelos livros didáticos destinados ao Ensino Médio, em um determinado período de tempo (1929-2004), através do estudo do desenvolvimento histórico dos conceitos químicos envolvidos neste tema. Outro objetivo foi o de identificar as concepções sobre ciência veiculadas pelos livros didáticos ao tratarem o tema Cinética Química. O modelo adotado para a análise dos livros didáticos está baseado na linha de pesquisa desenvolvida por Níaz (2001) e Justi (1997; 1999), que se baseia na história e filosofia da ciência para entender o tratamento dado aos conceitos químicos pelo livro didático. Para isso, foi utilizada a metodologia de Imre Lakatos, da reconstrução racional do conhecimento científico, para analisar a evolução histórica das idéias sobre Cinética Química. A reconstrução histórica foi feita a partir de pesquisas de historiadores da ciência, artigos de pesquisadores e artigos originais dos cientistas que estiveram envolvidos no estudo da cinética química. Foram propostos quatro Programas de Investigação Científica que representam o conhecimento científico sobre a Cinética Química no período de 1850 até 1935...

Desenvolvimento do metodo multivariado acelerado para determinação do prazo de validade de produtos unindo quimiometria e cinetica quimica; Development of the multivariate accelerated shelf-life test for determining the shelf-life of products using chemometrics and chemical kinetics

Andre Messias Krell Pedro
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 30/03/2009 PT
Relevância na Pesquisa
46.17%
DESENVOLVIMENTO DO MÉTODO MULTIVARIADO ACELERADO PARA DETERMINAÇÃO DO PRAZO DE VALIDADE DE PRODUTOS UNINDO QUIMIOMETRIA E CINÉTICA QUÍMICA descreve um novo conceito de análise de dados que permite avaliar os mecanismos que governam a degradação de bens de consumo e determinar o período de tempo no qual os bens de consumo mantém suas características dentro de níveis aceitáveis. O algoritmo une técnicas quimiométricas com a teoria cinética química formal, constituindo um avanço sobre os protocolos para determinação da validade de produto existentes. Além de ser de fácil interpretação, suas principais vantagens incluem a capacidade de unir informações provenientes de diferentes disciplinas – analíticos, físico-químicos, sensoriais - e a possibilidade de utilização direta de dados oriundos de instrumentação analítica como espectroscópios, cromatógrafos, calorímetros, etc. O trabalho é dividido em seis capítulos. O Capítulo I traz uma revisão da cinética química e dos métodos convencionais para determinação do prazo de validade de produtos. O algoritmo do Método Multivariado Acelerado, bem como suas premissas, vantagens e desvantagens, são descritos no capítulo II. Os Capítulos III e IV trazem aplicações do Método Multivariado Acelerado. No Capítulo III dados físico-químicos e sensoriais foram utilizados para determinar o prazo de validade de um produto alimentíco. No Capítulo IV utilizaram-se dados instrumentais...

Enhanced identification and exploitation of time scales for model reduction in stochastic chemical kinetics

Gómez-Uribe, Carlos A.; Verghese, George C.; Tzafriri, Abraham R.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.17%
Widely different time scales are common in systems of chemical reactions and can be exploited to obtain reduced models applicable to the time scales of interest. These reduced models enable more efficient computation and simplify analysis. A classic example is the irreversible enzymatic reaction, for which separation of time scales in a deterministic mass action kinetics model results in approximate rate laws for the slow dynamics, such as that of Michaelis–Menten. Recently, several methods have been developed for separation of slow and fast time scales in chemical master equation (CME) descriptions of stochastic chemical kinetics, yielding separate reduced CMEs for the slow variables and the fast variables. The paper begins by systematizing the preliminary step of identifying slow and fast variables in a chemical system from a specification of the slow and fast reactions in the system. The authors then present an enhanced time-scale-separation method that can extend the validity and improve the accuracy of existing methods by better accounting for slow reactions when equilibrating the fast subsystem. The resulting method is particularly accurate in systems such as enzymatic and protein interaction networks, where the rates of the slow reactions that modify the slow variables are not a function of the slow variables. The authors apply their methodology to the case of an irreversible enzymatic reaction and show that the resulting improvements in accuracy and validity are analogous to those obtained in the deterministic case by using the total quasi-steady-state approximation rather than the classical Michaelis–Menten. The other main contribution of this paper is to show how mass fluctuation kinetics models...

Sensitivity, robustness, and identifiability in stochastic chemical kinetics models

Komorowski, Michał; Costa, Maria J.; Rand, David A.; Stumpf, Michael P. H.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.13%
We present a novel and simple method to numerically calculate Fisher information matrices for stochastic chemical kinetics models. The linear noise approximation is used to derive model equations and a likelihood function that leads to an efficient computational algorithm. Our approach reduces the problem of calculating the Fisher information matrix to solving a set of ordinary differential equations. This is the first method to compute Fisher information for stochastic chemical kinetics models without the need for Monte Carlo simulations. This methodology is then used to study sensitivity, robustness, and parameter identifiability in stochastic chemical kinetics models. We show that significant differences exist between stochastic and deterministic models as well as between stochastic models with time-series and time-point measurements. We demonstrate that these discrepancies arise from the variability in molecule numbers, correlations between species, and temporal correlations and show how this approach can be used in the analysis and design of experiments probing stochastic processes at the cellular level. The algorithm has been implemented as a Matlab package and is available from the authors upon request.

Kinetics and diffusion in hydrodemetallation of nickel and vanadium porphyrins

Agrawal, Rakesh
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 422 leaves; 20966181 bytes; 20965934 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
56.01%
by Rakesh Agrawal.; Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1980.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.; Bibliography: leaves 268-376.

Oxidation kinetics of methylphosphonic acid in supercritical water : experimental measurements and model development

Sullivan, Patricia A. (Patricia Ann), 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 219 leaves; 17154789 bytes; 17183411 bytes; application/pdf; application/pdf
EN_US
Relevância na Pesquisa
46.16%
(cont.) at well-defined operating conditions and to develop. both microscopic and macroscopic models, ranging from regressed global models to an elementary reaction mechanism, to quantify MPA oxidation kinetics in supercritical water. MPA hydrolysis and oxidation rates were experimentally measured in a laboratory-scale plug flow reactor. The effects of MPA concentration (0.5 to 1.0 mM), oxygen concentration (1.0 to 3.8 mM), temperature (478 to 572⁰C) and pressure (138 to 277 bar) on oxidation rates were determined for residence times ranging from 3.0 to 9.5 s. Conversion due to hydrolysis was less than 6% after [tau]=7 s at all temperatures studied. For [tau]=7 s at stoichiometric conditions and P=246 bar, low conversion (X<30% at [tau]=10 s) was observed at T<503⁰C, while almost complete conversion (X=99%) occurred at T=571⁰C. The only phosphorus-containing product was phosphoric acid, while the carbon-containing intermediates, carbon monoxide and methane, were present in varying concentrations in addition to final carbon-containing product, carbon dioxide. Methane was only a minor product, with a carbon yield less than 20% at all experimental conditions. MPA oxidation rates varied with oxygen concentration and pressure (or water density)...

Swelling, mass transport, and chemical kinetics in bituminous coal pyrolysis

Hsu, Jaanpyng
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (390 leaves)
ENG
Relevância na Pesquisa
55.87%
by Jaanpyng Hsu.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1989.; Includes bibliographical references (leaves 330-340).

Development of novel methodologies to analyze the adsorption kinetics of nonionic surfactants

Moorkanikkara, Srinivas Nageswaran
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 276 p.
ENG
Relevância na Pesquisa
46.22%
When an aqueous surfactant solution is exposed to a clean water/air surface, it takes a finite time for the surfactant molecules to physically transport from the bulk aqueous solution to the surface in order to adsorb and reduce the surface tension. The time scales associated with the reduction in surface tension can vary between milliseconds to hours depending on the surfactant type and its concentration. Accordingly, development of a fundamental understanding of the underlying physical phenomena involved in the kinetics of surfactant adsorption will help to: (i) understand the observed Dynamic Surface Tension (DST) behavior of surfactants, and (ii) design optimal surfactant formulations for applications in which the surfactant adsorption kinetics plays a significant role in determining the effectiveness of the formulation. This thesis deals with modeling the adsorption kinetics of nonionic surfactants at prernicellar surfactant concentrations. Traditionally, the adsorption kinetics of nonionic surfactants at premicellar surfactant concentrations has been understood in the context of two models: (1) the diffusion-controlled model, which assumes that diffusion of surfactant molecules from the bulk solution to the surface is the rate-limiting step...

Ultraviolet disinfection kinetics for potable water production.

Amos, Steve A.
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2008
Relevância na Pesquisa
46.12%
Irradiation with ultraviolet (UV) light is used for the disinfection of bacterial contaminants in the production of potable water, and in the treatment of selected wastewaters. However, efficacy of UV disinfection is limited by the combined effect of suspended solids concentration and UV absorbance. Limited published UV disinfection data are available that account for the combined effects of UV dose, suspended solids concentration and UV absorbance. This present lack of a rigorous quantitative understanding of the kinetics of UV disinfection limits process optimisation and wider application of UV treatment. The development and validation of an adequate model to describe UV disinfection kinetics presented in this thesis can therefore be justified by an increased confidence of reliability of design for UV disinfection. Using the published data of Nguyen (1999), four established model forms were assessed to account for the combined effect of suspended solids and/or soluble UV absorbing compounds, and UV dose on the efficacy of disinfection. The four model forms were: a log-linear form, Davey Linear-Arrhenius (DL-A), Square-Root (or Ratkowsky- Belehradek) and a general nth order Polynomial (nOP) form that was limited to a third order. Criteria for assessment of an adequate predictive model were established including: accuracy of predicted against observed values...

Simulation of biodiesel and petrodiesel pollutant kinetics

Cai, G.; Abraham, J.
Fonte: The Modelling and Simulation Society of Aust & NZ; Australia Publicador: The Modelling and Simulation Society of Aust & NZ; Australia
Tipo: Conference paper
Publicado em //2013 EN
Relevância na Pesquisa
46.2%
Biodiesel is considered as an attractive alternative to petrodiesel for transportation applications. Substituting petrodiesel with domestically produced biodiesel increases energy independence, reduces the carbon footprint, and offers a viable path toward biomass utilisation. It has been found that biodiesel-fuelled engines emit up to 70% lower particulate matter (PM) compared to petrodiesel-fuelled engines, although they emit up to 20% more nitric oxides (NOx). In this study, simulations are employed to improve the fundamental understanding of biodiesel and petrodiesel combustion under pressure and temperature conditions in engines. n-Heptane is used as the surrogate for petrodiesel fuel and a ternary mixture of methyl decanoate, methyl-9-decenoate, and n-heptane as the surrogate for biodiesel fuel. The choice of chemical kinetic mechanism is a compromise between computational time and accuracy. Four mechanisms are evaluated and a 160-species skeletal chemical kinetic mechanism is employed to model the oxidation of n-heptane. The computational time is shown to increase dramatically as the complexity of the mechanism increases. Soot kinetics is represented using a chemical mechanism that models the growth of soot precursors starting from a single aromatic ring and growing by hydrogen abstraction and carbon (acetylene) addition. NOx kinetics is represented using the thermal...

Using the reactions O+H2 → OH+H to explore the importance of the atomic quantum states on chemical kinetics and reaction dynamics

Rio, Carolina; Brandão, João; Wang, Wenli
Fonte: Horizon Research Publishing Publicador: Horizon Research Publishing
Tipo: Artigo de Revista Científica
Publicado em /06/2015 ENG
Relevância na Pesquisa
55.97%
The O + H2 reaction is a particular example to alert the importance of a clear definition of the quantum state of an atom when referring to a chemical reaction. In its ground state, O (3P), the oxygen atom reacts with H2 through an energy barrier with small rate constant. In contrast, when the oxygen atom is in its first excited state, O (1D), the reaction O + H2 occurs without energy barrier and the rate constant is seven orders of magnitude higher. The dynamic behaviour of this reaction depends also on the quantum state of the oxygen atom.

Building robust chemical reaction mechanisms : next generation of automatic model construction software

Song, Jing, 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 319 p.; 21541413 bytes; 21541212 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
56.14%
Building proper reaction mechanisms is crucial to model the system dynamic properties for many industrial processes with complex chemical reaction phenomena. Because of the complexity of a reaction mechanism, computer-aided reaction mechanism generation software appeared in recent years to help people efficiently build large reaction mechanisms. However, the limitations of those programs, such as not being able to model different types of reaction systems and to provide sufficiently precise thermodynamic and kinetic parameters impede their broad usage in real reaction system modeling. Targeting the drawbacks in current first-generation reaction modeling software, this thesis presents the second-generation of reaction mechanism construction software, Reaction Mechanism Generator, (RMG). In RMG, a new reaction template method is proposed to help quickly and flexibly define different types of reaction families, so that users can easily characterize any reaction system of interest without modifying the software. Furthermore, this work also presents new functional group tree approaches to construct hierarchical structured thermodynamics and kinetics databases for managing a large number of parameters, so that people are able to quickly and precisely identify better kinetics for different reactions in the same reaction family and to easily extend and update the databases with the latest research results. This new data-model dramatically improves the interface between the chemistry and computer science...

Design of a viable homogeneous-charge compression-ignition (HCCI) engine : a computational study with detailed chemical kinetics

Yelvington, Paul E., 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 261 p.; 1558221 bytes; 1644212 bytes; application/pdf; application/pdf
EN_US
Relevância na Pesquisa
55.89%
The homogeneous-charge compression-ignition (HCCI) engine is a novel engine technology with the potential to substantially lower emissions from automotive sources. HCCI engines use lean-premixed combustion to achieve good fuel economy and low emissions of nitrogen-oxides and particulate matter. However, experimentally these engines have demonstrated a viable operating range that is too narrow for vehicular applications. Incomplete combustion or misfire can occur under fuel-lean conditions imposing a minimum load at which the engine can operate. At high loads, HCCI engines are often extremely loud and measured cylinder pressures show strong acoustic oscillations resembling those for a knocking sparkignited engine. The goal of this research was to understand the factors limiting the HCCI range of operability and propose ways of broadening that range. An engine simulation tool was developed to model the combustion process in the engine and predict HCCI knock and incomplete combustion. Predicting HCCI engine knock is particularly important because knock limits the maximum engine torque, and this limitation is a major obstacle to commercialization. A fundamentally-based criterion was developed and shown to give good predictions of the experimental knock limit. Our engine simulation tool was then used to explore the effect of various engine design parameters and operating conditions on the HCCI viable operating range. Performance maps...

Theory of Chemical Kinetics and Charge Transfer based on Nonequilibrium Thermodynamics

Bazant, Martin Z.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.22%
Classical theories of chemical kinetics assume independent reactions in dilute solutions, whose rates are determined by mean concentrations. In condensed matter, strong interactions alter chemical activities and create inhomogeneities that can dramatically affect the reaction rate. The extreme case is that of a reaction coupled to a phase transformation, whose kinetics must depend on the order parameter -- and its gradients, at phase boundaries. This Account presents a general theory of chemical kinetics based on nonequilibrium thermodynamics. The reaction rate is a nonlinear function of the thermodynamic driving force (free energy of reaction) expressed in terms of variational chemical potentials. The Cahn-Hilliard and Allen-Cahn equations are unified and extended via a master equation for non-equilibrium chemical thermodynamics. For electrochemistry, both Marcus and Butler-Volmer kinetics are generalized for concentrated solutions and ionic solids. The theory is applied to intercalation dynamics in the phase separating Li-ion battery material Li$_x$FePO$_4$.; Comment: research account, 17 two-column pages, 12 figs, 78 refs - some typos corrected Accounts of Chemical Research (2013)

Molecular Energy Relations From Chemical Kinetics

Finkel, Robert W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
56.01%
Since molecular energy transformations are responsible for chemical reaction rates at the most fundamental level, chemical kinetics should provide some information about molecular energies. This is the premise and objective of this note. We describe a Hamiltonian formulation for kinetic rate equations where the concentrations are the generalized coordinates and the conjugate momenta are simply related to individual average molecular energies. Simple examples are presented and the resulting energy relations naturally include non-equilibrium reactions. An analysis predicts the reasonable outcome that thermal agitation of a composite molecule increases its rate of dissociation.; Comment: 4 pages

Advanced quasi-steady state approximation for chemical kinetics

Girimaji, Sharath; Ibrahim, Ashraf
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.97%
Computational feasibility of turbulent reacting flows hinges on the reduction of large chemical kinetics systems to smaller more manageable reaction sets. Recently, several sophisticated reduction techniques have been developed but they continue to be computationally prohibitive for practical three-dimensional unsteady computations. For such applications, the classical quasi-steady state assumption (QSSA), despite serious shortcomings, continues to be popular due to its conceptual clarity and computational simplicity. Starting from invariant manifold description, we develop an advanced quasi-steady state assumption which (i) is independent of the choice of the retained (slow) species; (ii) possesses much improved physical and mathematical characteristics; and (iii) can be specialized for any objective function.; Comment: I will submit a different work in this topic

Method of invariant manifold for chemical kinetics

Gorban, Alexander N.; Karlin, Iliya V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/07/2002
Relevância na Pesquisa
56.08%
In this paper, we review the construction of low-dimensional manifolds of reduced description for equations of chemical kinetics from the standpoint of the method of invariant manifold (MIM). MIM is based on a formulation of the condition of invariance as an equation, and its solution by Newton iterations. A review of existing alternative methods is extended by a thermodynamically consistent version of the method of intrinsic low-dimensional manifolds. A grid-based version of MIM is developed, and model extensions of low-dimensional dynamics are described. Generalizations to open systems are suggested. The set of methods covered makes it possible to effectively reduce description in chemical kinetics.; Comment: 41 pages, 1 figure

Sensitivity, robustness and identifiability in stochastic chemical kinetics models

Komorowski, Michal; Costa, Maria J.; Rand, David A.; Stumpf, Michael
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/04/2011
Relevância na Pesquisa
46.13%
We present a novel and simple method to numerically calculate Fisher Information Matrices for stochastic chemical kinetics models. The linear noise approximation is used to derive model equations and a likelihood function which leads to an efficient computational algorithm. Our approach reduces the problem of calculating the Fisher Information Matrix to solving a set of ordinary differential equations. {This is the first method to compute Fisher Information for stochastic chemical kinetics models without the need for Monte Carlo simulations.} This methodology is then used to study sensitivity, robustness and parameter identifiability in stochastic chemical kinetics models. We show that significant differences exist between stochastic and deterministic models as well as between stochastic models with time-series and time-point measurements. We demonstrate that these discrepancies arise from the variability in molecule numbers, correlations between species, and temporal correlations and show how this approach can be used in the analysis and design of experiments probing stochastic processes at the cellular level. The algorithm has been implemented as a Matlab package and is available from the authors upon request.

Percepção de alunos do ensino médio sobre a temática conservação dos alimentos no processo de ensino-aprendizagem do conteúdo cinética química

Silva,Antonio Denilson Leandro da; Vieira,Elizabeth do Rosário; Ferreira,Wagner Pinheiro
Fonte: Universidad Nacional Autónoma de México, Facultad de Química Publicador: Universidad Nacional Autónoma de México, Facultad de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2013 PT
Relevância na Pesquisa
46.17%
This article derives from a survey of second graders from high school in a public school located in São Miguel do Guama, Pará It on the perceptions of students on the theme of food preservation in the process of teaching and learning content of chemical kinetics. It deals with the perceptions of students on the theme of food preservation in the process of teaching and learning of the content of chemical kinetics. Our aim in framing questions pertaining to this article was the fact that seek to identify the methodology used by the teacher allowed the student to have an understanding of the practical situations of everyday life that require the taking of certain decisions and if they could establish a relationship between the topic addressed with the specific content of chemistry, based on everyday observations. To this end, there was the application of 25 questionnaires for data collection. The data showed us that the majority (68%) gives students failed to articulate the theme food preservation with the chemical kinetics. This leads us to infer that the use of alternative methodologies in teaching chemistry, and the improvement of students' preconceptions are important in the process of teaching and learning of chemical content.