Pedagogical Content Knowledge of Chemical Kinetics: Experiment

Commentary Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

pubs.acs.org/jchemeduc

Pedagogical Content Knowledge of Chemical Kinetics: Experiment Selection Criteria To Address Students’ Intuitive Conceptions Ainoa Marzabal,*,† Virginia Delgado,‡ Patricia Moreira,† Lorena Barrientos,‡ and Jeannette Moreno‡ †

Facultad de Educación, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago de Chile, Chile Facultad de Química, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago de Chile, Chile

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‡

ABSTRACT: Learning the key concepts of chemical kinetics is a challenge for higher education students. These difficulties are due, among other things, to the fact that traditional teaching does not consider the findings of research on students’ learning in this particular domain of chemistry. In this commentary, we propose research-based criteria for the selection of experiments that respond to the learning difficulties in chemical kinetics that have been widely reported in recent years. Additionally, we discuss a teaching strategy that may be appropriate to favor the evolution of students’ intuitive conceptions by evaluating their ideas and those of their peers in the analysis of scientific evidence.

KEYWORDS: First-Year Undergraduate/General, Hands-On Learning/Manipulatives, Kinetics, Misconceptions/Discrepant Events, Constructivism, Learning Theories

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INTRODUCTION A variety of research studies have shown that the topic of chemical kinetics is perceived by students as one of the most difficult subjects in general and physical chemistry courses.1 Although mathematics proficiency issues affect students’ understanding of key ideas,2 many of the difficulties that students face are conceptual in nature. Unfortunately, traditional teaching practices fail to address these challenges as they are often not informed by research findings on students’ learning in this specific domain.3 An analysis of students’ conceptions and their evolution with instruction is necessary to raise pedagogical criteria for the teaching of chemical kinetics.3 These pedagogical criteria can be integrated with disciplinary criteria that guide decisionmaking in traditional teaching practices.4 The knowledge that emerges from this integration is known as pedagogical content knowledge (PCK); it strengthens a teacher’s ability to foster student understanding of specific topics.5,6 The PCK of chemistry teachers determines the choices they make about what concepts are important to teach, what kinds of questions or problems to pose, instruments they use to assess student understanding, and the interpretations they generate of their students’ ideas.7 PCK also influences teachers’ decisions about what laboratory experiments can best help students understand complex chemistry concepts. In this commentary, we introduce a research-based tool to facilitate instructors’ selection of experiments to more effectively challenge students’ intuitive conceptions, helping them develop meaningful understandings.8,9 © XXXX American Chemical Society and Division of Chemical Education, Inc.

SELECTION CRITERIA

Bain and Towns have summarized the research literature on students’ understanding of chemical kinetics at the secondary and tertiary levels.10 The authors present their findings associating the learning difficulties reported in the literature with the enduring understandings in chemical kinetics defined in the General Chemistry Anchoring Concepts Content Map developed by Holme and collaborators.11 This organization creates links between disciplinary content knowledge (CK) and pedagogical content knowledge (PCK) about students’ ideas. A detailed description of this articulation is shown in Table 1 for the enduring understandings that laboratory work can help develop. The enduring understandings listed in Table 1 are used in this commentary to organize the description and discussion of criteria that teachers can use to select experiments that challenge and address the common intuitive conceptions associated with each of the listed understandings. These criteria are summarized in Table 2 and described in the following paragraphs. Received: April 24, 2018 Revised: July 9, 2018

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DOI: 10.1021/acs.jchemed.8b00296 J. Chem. Educ. XXXX, XXX, XXX−XXX

Pedagogical Content Knowledge (PCK) about students' ideas

Student Misconception Examples

See ref 12. bSee ref 13. cSee ref 14. dSee ref 15. eSee ref 16.

B

a

Assume all reactions are elementary

4

Students’ Expectations

The reaction order coincides with the stoichiometric coefficient of the chemical equation When the temperature is increased, the rate of the exothermic reaction decreases The chemical species present in a reaction are only the reactants and products As the order of reaction depends on the reaction mechanism, it will not vary when adding a catalyst As the mechanism is not affected, the same intermediates can be identified

The reaction rate increases proportionally to the increase of concentration

See ref 10. bSee ref 17. cSee ref 18. dSee ref 19. eSee ref 20. fSee ref 21. gSee ref 22.

6

5

Assume that catalysts decrease the activation energy without affecting the mechanism of the reaction

Assume that the exponents of the reactants’ concentration in the rate equation are equal to the stoichiometric coefficients Apply the Le Châtelier principle to predict the effect of temperature on the reaction rate

2

3

Assume linear relation between concentration of reactant/product and reaction rate

Intuitive Conceptiona

1

Criterion Number

Intermediate without catalyst ≠ catalyst intermediate with catalyst

Order without catalyst ≠ order with catalyst

Reaction intermediate can be identified

Exothermic, ΔH < 0

As the catalyst affects the mechanism of the reaction, the reaction intermediates vary.

The order and the stoichiometric coefficient do not always coincide (only when the reaction is elemental). An increase in temperature increases the rate, regardless of whether it is exothermic or endothermic. The chemical species present in a reaction are the reactants, reaction intermediates, and products (except when the reaction is elemental). As the catalyst affects the mechanism of the reaction, the reaction order may vary.

Order ≠ stoichiometric coefficient

Conceptions from Experimental Evidence The relationship between reaction rate and concentration depends on the order of reaction.

Order ≠ 1

Selection Criterion

Misconceptions in the exploding flask demonstration resolved through students’ critical thinkingg

Ruthenium(VI)-catalyzed oxidation of alcohols by hexacyanoferrate (III)f

Model experiment of thermal runaway reactions using the aluminum−hydrochloric acid reactiond Epoxidation of 2,5-di-tert-butyl-1,4-benzoquinonee

Effect of temperature and ionic strength on the oxidation of iodide by iron(III): A clock reaction kinetic studyb Glyoxal clock reactionc

Example Reaction

Table 2. Summary of Students’ Intuitive Conceptions and Expectations, Criteria To Select Experiments, and Conceptions Arising from Experimental Evidence

a

Increasing the concentration of reactants proportionally increases Rate is generally defined as the change in concentration of a reactant or product as Students often assume a linear relationship between the concentration of a reactant or product and the reaction rate. the reaction rate. a function of time.a The “order” of a reaction is derived from the exponent on the concentration term Students often assume that the exponents of the reactants The order of a chemical reaction can be deduced from the balanced of a given reactant in the rate law.b concentration in the rate equation are equal to the stoichiometric chemical equation. coefficients. The temperature dependence of the reaction rate is contained in the rate constant. Students often apply the Le Châtelier’s principle to predict the effect When the temperature is increased, the rate of the endothermic This temperature dependence is often well modeled by the Arrhenius model.c of temperature on the reaction rate. reactions increases, but the rate of the exothermic reaction decreases. It is possible to devise a series of reactions that, when summed, yield the overall Students often assume all chemical reactions are elementary (no There is conflation of “intermediate” and “activated complex” d reaction and provide a mechanism for how the reaction occurs. recognition of the slow step as the rate-determining step). conceptions. A catalyst increases the rate of the reaction by providing a new reaction pathway Students often assume that catalysts increase the yield of product. Adding a catalyst will increase the amount of product that is with a lower activation energy.e obtained. Students often assume that catalysts decrease the activation energy Because a catalyst lowers the activation energy, it affects both without affecting the mechanism of the reaction. forward and reverse reactions. Students often assume that the catalyst does not interact with any of A catalyst is needed to initiate the reaction but does not interact with the reactants or products. the reaction species; that is why only a small amount is needed.

Content Knowledge (CK)

Table 1. Relationship of Content Knowledge in the Form of Enduring Understandings in Chemical Kinetics and Associated Pedagogical Content Knowledge about Students’ Ideas with Specific Examples of Students’ Misconceptions

Journal of Chemical Education Commentary


Journal of Chemical Education

Commentary

CK 1: Rate Is Generally Defined as the Change in Concentration of a Reactant or Product as a Function of Time

CK 5: A Catalyst Increases the Rate of the Reaction by Providing a New Reaction Pathway with a Lower Activation Energy

Educational research indicates that students often consider that the rate of reaction is directly proportional to the concentration of any reactant.12 This assumption, however, is only valid when the reaction order for a particular substance is 1. In this sense instructors that are planning experiments related to only first order reactions are likely to reinforce this conception. Therefore, to address this intuitive conception, the instructors should engage students in the exploration of chemical reactions that do not follow first order kinetics (selection criterion 1: rate order ≠ 1).

The students have the assumption that the higher activation energy is, the lower the reaction rate is.16 The idea that chemical reactions with lower activation energy occur more quickly than those with higher activation energy is true when we compare reactions at similar temperatures. However, when the temperatures at which two chemical reactions occur are significantly different, it is possible that the reaction with the highest activation energy occurs more rapidly, according to the Ea/T ratio for the two reactions. In the laboratory, students can verify that at similar temperatures evidence confirms what they expect, and also that eventually, depending on the temperatures, the reaction with higher activation energy may be faster. For the first assumption associated with catalysis,12 students can verify that, by performing the same reaction with or without a catalyst, even if the time required is different, the same amount of product is obtained or the reaction ends at the same equilibrium point. When students have established different reaction orders with and without a catalyst, they will have evidence that the catalyst affects the reaction mechanism. When the order of reactions coincides, it may also be possible to identify different intermediates in the reaction. Thus, a criterion concerning catalysts would be to select reactions in which the reaction order without a catalyst is different from the order of reaction with a catalyst (criterion 5: order without catalyst ≠ order with catalyst). It would also be possible to demonstrate the change in the mechanism by identifying experimentally that different intermediates appear in the reaction (criterion 6: intermediate without catalyst ≠ intermediate with catalyst).

CK 2: The “Order” of a Reaction Is Derived from the Exponent on the Concentration Term of a Given Reactant in the Rate Law

It is common for students to think that the order of the reaction with respect to any substance involved in the process is equal to the stoichiometric coefficient represented in the balanced overall chemical reaction.13 To address this conception, it would be important to engage in experiments with chemical reactions in which the rate order and the stoichiometric coefficient for the reactant do not have the same value (selection criterion 2: rate order ≠ stoichiometric coefficient). CK 3: The Temperature Dependence of the Reaction Rate Is Contained in the Rate Constant; This Temperature Dependence Is Often Well Modeled by the Arrhenius Model

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Regarding this criterion, the Arrhenius model provides evidence of the temperature dependence of the rate constant, according to a natural exponential relation.14 Under the Arrhenius model, an increase in temperature implies an increment in the reaction rate, regardless of it being exothermic or endothermic. To address this conception, it would be necessary to verify that the reaction rates increase with the temperature, even if the reaction is exothermic (criterion 3: exothermic, ΔH > 0). To verify that the activation energy of a reaction remains constant when the temperature is modified, the students can establish it through the Arrhenius equation or graphically by representing ln k as a function of 1/T.

TEACHING STRATEGY TO ADDRESS MISCONCEPTIONS It is expected that the proposed criteria contribute to the pedagogical content knowledge of chemical kinetics since they allow us to select experiments that respond to the intuitive conceptions of the students. Thus, to apply these criteria, it is necessary to identify students’ ideas through diagnostic assessment strategies, and to manage activities associated with experimental work that favor the evolution of those ideas.23 In the literature, we have found a good number of teaching proposals to guide activities for the learning of kinetics that include experimentation. These proposals can be classified, according to the pedagogical perspective on which they are based: constructivism,14 conceptual change,16,24 problembased learning,25 case studies,26 inquiry,27 and modeling.2 From our perspective the intuitive conceptions of students can be conceived as mental models, which are structural analogies of objects, events, processes, or ideas that allow students to reason when explaining phenomenon. 28,29 Modeling, understood as the evolution of mental models,24 is favored when instructors provide students with learning environments for working with their peers, identifying individual differences, testing their own conceptions, and incorporating new ideas that arise from the interaction.30 In modeling-based teaching, which is enacted on the basis of the socio-constructivist perspective of learning, enduring understandings are achieved as the result of interactions among students, teachers, and learning resources.31 The

CK 4: It Is Possible To Devise a Series of Reactions That, When Summed, Yield the Overall Reaction and Provide a Mechanism for How the Reaction Occurs

For the assumption that all reactions are elementary,15 those reactions have a distinctive feature: The molecularity (the number of molecules involved in the reaction) coincides with the total stoichiometry of the reaction (the addition of the stoichiometric coefficients of the reactants) and the reaction order (the addition of the exponents in the rate equation). From this conception two selection criteria emerge: The reaction is not elementary; that is, the stoichiometric coefficients and reaction orders do not coincide, as seen in criterion 2. Also, it is possible to experimentally identify some reaction intermediate (criterion 4: at least one reaction intermediate can be identified experimentally) when the reaction is not elementary. C



Commentary

chemical kinetics. However, it is necessary to continue deepening the analysis of what we already know about how students learn kinetics, as well as other domains of chemistry that have proven to be challenging, to strengthen the processes of instruction and achieve enduring understandings in higher education students.

teaching strategy is structured to promote environments and activities in which students express, evaluate, review, and apply their ideas, as well as the ideas of their peers.32 The modeling sequence, which we present in Figure 1, although not specific to the learning of chemical kinetics,

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Ainoa Marzabal: 0000-0003-0108-5889 Patricia Moreira: 0000-0002-2055-6124 Lorena Barrientos: 0000-0002-9641-6507 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the support of Vicente Talanquer. REFERENCES

(1) Sö zbilir, M. What Makes Physical Chemistry Difficult? Perceptions of Turkish Chemistry Undergraduates and Lecturers. J. Chem. Educ. 2004, 81 (4), 573−578. (2) Justi, R. Teaching and Learning Chemical Kinetics. In Chemical Education: Towards Research-Based Practice; Gilbert, J. K., de Jong, O., Justi, R., Treagust, D. F., van Driel, J. H., Eds.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 2002; pp 293−315. (3) Teo, T. W.; Goh, M. T.; Yeo, L. W. Chemistry Education Research Trends: 2004−2013. Chem. Educ. Res. Pract. 2014, 15 (4), 470−487. (4) Gess-Newsome, J.; Carlson, J. A Report on the PCK Summit: Current and Future Research Directions. Symposium at the 2013 NARST Annual International Conference, Rio Grande, Puerto Rico, April 6−9, 2013. https://bscs.org/sites/default/files/_media/community/ downloads/a_report_on_the_pck_summit_narst_2013.pdf (accessed Jul 2018). (5) Shulman, L. S. Those Who Understand: Knowledge Growth in Teaching. Educ. Res. 1986, 15 (2), 4−14. (6) Abell, S. K. Research on Science Teacher Knowledge. In Handbook of Research on Science Education; Abell, S. K., Lederman, N. G., Eds.; Lawrence Erlbaum: Mahwah, NJ, 2007; pp 1105−1149. (7) Talanquer, V. Formación Docente: Qué Conocimiento ́ ́ Distingue a Los Buenos Maestros de Quimica? Educ. Quimica 2003, 15 (1), 60−66. (8) Chairam, S.; Somsook, E.; Coll, R. K. Enhancing Thai Students’ Learning of Chemical Kinetics. Res. Sci. Technol. Educ. 2009, 27 (1), 95−115. (9) Alvarado, C.; Cañada, F.; Garritz, A.; Mellado, V. Canonical Pedagogical Content Knowledge by CoRes for Teaching Acid−Base Chemistry at High School. Chem. Educ. Res. Pract. 2015, 16 (3), 603− 618. (10) Bain, K.; Towns, M. H. A Review of Research on the Teaching and Learning of Chemical Kinetics. Chem. Educ. Res. Pract. 2016, 17 (2), 246−262. (11) Holme, T.; Luxford, C.; Murphy, K. Updating the General Chemistry Anchoring Concepts Content Map. J. Chem. Educ. 2015, 92 (6), 1115−1116. (12) Yalcinkaya, E.; Tastan-Kirik, O.; Boz, Y.; Yildiran, D. Is CaseBased Learning an Effective Teaching Strategy to Challenge Students’ Alternative Conceptions Regarding Chemical Kinetics? Res. Sci. Technol. Educ. 2012, 30, 151−172. (13) Cakmakci, G.; Aydogdu, C. Designing and Evaluating an Evidence-Informed Instruction in Chemical Kinetics. Chem. Educ. Res. Pract. 2011, 12, 15−28.

Figure 1. Modeling sequence to favor the evolution of students’ initial models on chemical kinetics.

provides orientations that are appropriate to favor the evolution of students’ intuitive ideas on that topic through experimentation.33 Initially, we expect instructors to apply diagnostic assessment instruments or questions that allow them to know the students’ initial conceptions about kinetics23 (conception elicitation). Once the instructors can identify the initial models of their students, they can lead a productive discussion in which the students recognize the presence of different conceptions in the classroom and evaluate them in the prediction and explanation of phenomena (conception recognition). Afterward, instructors select the conceptions they consider most relevant and choose an experiment that, according to the proposed criteria, allows those concepts to be addressed. Then, students develop the experimental activity in which empirical evidence that can be contrasted with the ideas expressed by students in the previous stages is gathered. In the discussion of results, students contrast initial predictions with the data collected in the experimental activity, focusing on the selected conceptions to promote evolution of students’ ideas (discussion of results). Finally, instructors provide instances that allow students to recognize the limitations of their initial models, and analyze the evolution of their ideas throughout the class (metacognition).

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FINAL COMMENTS The proposed criteria for selecting experiments can guide the decisions of the instructors in addressing chemical kinetics, integrating the pedagogical and disciplinary domain. Instructors can use the criteria described to make better instructional decisions in terms of the experiments and teaching strategies that would better support students’ learning. The ideas presented in this commentary contribute to the pedagogical content knowledge as a framework for teaching D



Commentary

(14) Kurt, S.; Ayas, A. Improving Students’ Understanding and Explaining Real Life Problems on Concepts of Reaction Rate by Using a Four Step Constructivist Approach. Energy Educ. Sci. Technol. Part B: Soc. Educ. Stud. 2012, 4, 979−992. (15) Turányi, T.; Tóth, Z. Hungarian University Students’ Misunderstanding in Thermodynamics and Chemical Kinetics. Chem. Educ. Res. Pract. 2013, 14, 105−116. (16) Tastan-Kirik, Ö . T.; Boz, Y. Cooperative Learning Instruction for Conceptual Change in the Concepts of Chemical Kinetics. Chem. Educ. Res. Pract. 2012, 13, 221−236. (17) Bauer, J.; Tomisic, V.; Vrkljan, P. B. A. The Effect of Temperature and Ionic Strength on the Oxidation of Iodide by Iron(III): A Clock Reaction Kinetic Study. J. Chem. Educ. 2012, 89, 540−544. (18) Ealy, J. B.; Negron, A. R.; Stephens, J.; Stauffer, R.; Furrow, S. D. The Glyoxal Clock Reaction. J. Chem. Educ. 2007, 84, 1965−1967. (19) Kitabayashi, S.; Nakano, M.; Nishikawa, K.; Koga, N. Model Experiment of Thermal Runaway Reactions Using the Aluminum− Hydrochloric Acid Reaction. J. Chem. Educ. 2016, 93, 1261−1266. (20) Hairfield, E. M.; Moomaw, E. W.; Tamburri, R. A.; Vigil, R. A. The Epoxidation of 2,5-di-tert-butyl-1,4-benzoquinone: A Consecutive Reaction for the Physical Chemistry Laboratory. J. Chem. Educ. 1985, 62, 175−177. (21) Mucientes, A. E.; de la Peña, M. A. Ruthenium(VI)-Catalyzed Oxidation of Alcohols by Hexacyanoferrate(III): An Example of Mixed Order. J. Chem. Educ. 2006, 83, 1643−1644. (22) Spierenburg, R.; Jacobse, L.; de Bruin, I.; van den Bos, D. J.; Vis, D. M.; Juurlink, L. B. F. Misconceptions in the Exploding Flask Demonstration Resolved through Students’ Critical Thinking. J. Chem. Educ. 2017, 94, 1209−1216. (23) Cakmakci, G. Identifying Alternative Conceptions of Chemical Kinetics among Secondary School and Undergraduate Stidents in Turkey. J. Chem. Educ. 2010, 87, 449−455. (24) Kingir, S.; Geban, Ö . The Effect of Conceptual Change Approach on Students’ Understanding of Reaction Rate Concepts. H. Ü . J. Educ. 2012, 43, 306−317. (25) Bodner, G. M.; Herron, J. D. Problem Solving in Chemistry. In Chemical Education: Towards Reasearch-Based Practice; Gilbert, J. K., De Jong, O., Justi, R., Treagust, D. F., Van Driel, J. H., Eds.; Kluwer Academic Publishers: Dordecht, Netherlands, 2003; pp 235−266. (26) YalÇ inkaya, E.; Tastan-Kirik, Ö ; Boz, Y.; Yildiran, D. Is CaseBased Learning an Effective Teaching Strategy to Challenge Students’ Alternative Conceptions Regarding Chemical Kinetics? Res. Sci. Technol. Educ. 2012, 30, 151−172. (27) Supasorn, S.; Promarak, V. Implementation of 5E Inquiry Incorporated with Analogy Learning Approach to Anhance Conceptual Understanding of Chemical Reaction Rate for Grade 11 Students. Chem. Educ. Res. Pract. 2015, 16, 121−132. (28) Vosniadou, S. Mental Models in Conceptual Development. In Model-Based Reasoning: Science, Technology, Values; Magnani, L., Nersessian, N. J., Eds.; Kluwer and Plenum: New York, 2002; pp 353−368. (29) Thagard, P. How Brains Make Mental Models. In Model-Based Reasoning in Science and Technology: Abduction, Logic, and Computational Discovery; Magnani, L., Carnieli, W., Pizzi, C., Eds.; Springer: Berlin, Germany, 2010; pp 447−461. (30) Nersessian, N. J. Creating Scientific Concepts; MIT Press: Cambridge, MA, 2008. (31) Gilbert, J. K.; Justi, R. Modelling-Based Teaching in Science Education; Springer International Publishing: Cham, Switzerland, 2016; Vol. 9. (32) Justi, R. Learning How To Model in Science Classroom: Key Teacher’s Role in Supporting the Development of Students’ Modelling Skills. Educ. Quim. 2009, 20 (1), 32−40. (33) Schwartz, M. Cognitive Development and Learning: Analyzing the Building of Skills in Classrooms. Mind, Brain, Educ. 2009, 3 (4), 198−208.

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Pedagogical Content Knowledge of Chemical Kinetics: Experiment

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