Article Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX
pubs.acs.org/jchemeduc
Investigation of Undergraduate and Graduate Chemistry Students’ Understanding of Thermodynamic Driving Forces in Chemical Reactions and Dissolution Kinsey Bain‡ and Marcy H. Towns*,† ‡
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
†
ABSTRACT: The concept of energy is of central significance, as it is a core disciplinary idea in chemistry and a cross-cutting concept in the sciences. This study sought to investigate student understanding of energetics and associated thermodynamic functions in chemical reactions and processes across a sample of introductory-level undergraduate chemistry students, upper-level undergraduate chemistry students, and physical chemistry graduate students. Participants were interviewed using an interview-about-events protocol, interacting with reagents that underwent chemical reactions or dissolutions. Analysis of the interview data revealed specific student difficulties with content, as well as common reasoning patterns used by students when considering energy changes in observed reactions and processes. Implications for curriculum and instruction are discussed. KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Upper-Division Undergraduate, Graduate Education/Research, Chemical Education Research, Hands-On Learning/Manipulatives, Misconceptions/Discrepant Events, Thermodynamics FEATURE: Chemical Education Research
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reveal many alternative conceptions and much interdisciplinary confusion.7,13−17 However, little is known about how students’ energy conceptions develop over time. Many studies have been conducted at the primary and ̈ reasoning patterns where secondary levels, revealing naive learners use everyday experience and language to describe physical and chemical phenomena. For example, children often view heat (and cold) as a substance that is transferred.18−20 Other work has been done to characterize energy conceptions, such as the energetic nature of chemical bonding21 or energy changes in reactions.22 Other studies have revealed that heat is often described by secondary students as something that is consumed in a chemical reaction or is a causal agent for chemical reactions.21,23,24 Studies of university students’ conceptions about heat and temperature reveal strong similarities to those in primary and secondary learners. For example, undergraduate students view temperature, heat, and cold as substances.1,8,25−28 Surprisingly, temperature and heat confusion has also been documented among graduate students, adults, and expert-level scientists.8,28
nergy is one of the most important themes in science, unifying various scientific disciplines.1,2 Not only does it serve as an explanatory tool for scientific causality,3 but also it is the key to understanding many societal issues.4−6 However, research on student understanding reveals that topics related to thermodynamics are difficult for students to correctly apply.7 Because incorrect understandings are highly resistant to change, they often persist to the graduate-level and beyond.8−10 On the basis of this research, the chemistry community has called for effective evidence-based pedagogical methods that facilitate the formation of scientifically accurate conceptions.10,11 Considering thermodynamic driving forces, this call is critical because energy is a chemistry disciplinary core idea and a cross-cutting concept for science, technology, and engineering disciplines.2 Targeting the teaching and learning of energy concepts is important for developing scientifically normative (or correct) understandings in future scientists and scientifically literate citizens alike.4−6,12
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BACKGROUND Discipline-based education researchers (DBERs) in fields such as chemistry, physics, biology, and engineering have a vested interest in helping students develop appropriate understandings of energy concepts which are relevant, useful, and insightful across disciplines.2,7 Investigations across these disciplines © XXXX American Chemical Society and Division of Chemical Education, Inc.
Received: November 14, 2017 Revised: February 16, 2018
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DOI: 10.1021/acs.jchemed.7b00874 J. Chem. Educ. XXXX, XXX, XXX−XXX
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Table 1. Talanquer’s Student Reasoning Framework41 Implicit Assumptions Categorization (implicit/explicit): nature of substance/process Inheritance Assumption: inherit properties from individual submicroscopic components Nature of Events: centralized causality (active/enabling) or teleology (intentional agents)
Heuristics Recognition: extent to which an object is recognized or known to exhibit properties Representativeness: assuming commonalities in properties/behaviors between similar objects One-Reason Decision Making: decision based on search from a single differentiating cue
of examination, affording deep insight into the knowledge and understanding of the participants. One of the benefits of using constructivism as a framework is that it did not restrict analysis, allowing themes to emerge from the data. A second framework was used to make sense of the patterns that were becoming apparent during data analysis. Talanquer’s41 student reasoning framework was selected, as it afforded important insight about common reasoning modalities and implications for instruction. This framework outlines six specific types of implicit assumptions or heuristics as shown in Table 1. Implicit assumptions are beliefs about the properties of entities or phenomenological behavior, which Talanquer classifies in three ways: categorization, inheritance assumption, and nature of events. Heuristics are short-cut reasoning strategies individuals use to make choices, which reduce the cognitive load and mental effort by minimizing the cues evaluated in the decision-making process. The Talanquer framework specifies three heuristic types: recognition, representativeness, and one-reason decision making.41
Various studies have explored undergraduate students’ ideas about bond energies. For example Boo21 has reported that students believe that bond forming requires energy and that bond breaking releases energy,15,24 a finding that is often attributed to intuitive ideas about building macroscopic structures or to biology instruction, where it is conventional to state that the breaking of a bond yields energy.14,15,24 This apparent alternative conception may not be as simple as it appears; Drefyus et al.15 provide data where students expand on this conception and attempt to reconcile multiple disciplinary approaches. Other research on undergraduate student understanding of thermodynamics concepts in various DBER fields has also been reported. Much of this is presented in reviews by Tsaparlis29 and Bain et al.7 A common finding is the conflation of thermodynamic state functions, such as enthalpy, entropy, and Gibbs free energy.30,31 These studies have demonstrated that everyday language or experiences are incorrectly used to justify or predict thermal phenomena,27,32,33 a finding that is corroborated in investigations on student understanding of entropy.34−36 Studies on undergraduate student understanding of Gibbs free energy are less common.7 Wolfson et al.37 investigated this in the context of biological chemical reactions. A key finding was that few students demonstrated difficulty recognizing that a negative ΔG indicates a thermodynamically spontaneous reaction, a result also reported by Carson and Watson.34 However, a common alternative conception was that an exothermic reaction is always spontaneous.37 This exothermic enthalpy/spontaneity conflation has been seen in other studies with both secondary and university students.32,38,39 Given the central importance of energy in chemistry and other science and engineering disciplines,2 we believe that a study that would yield further insight into student understanding of thermodynamic driving forces in chemical reactions and physical processes is warranted. An investigation of such understanding across student levels would be particularly insightful. Therefore, the guiding research question for this study is How do introductory-level undergraduate chemistry students, upper-level undergraduate chemistry students, and physical chemistry graduate students describe thermodynamic driving forces (such as energy, enthalpy, entropy, Gibbs f ree energy, spontaneity, etc.) in the context of common chemical reactions and processes?
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Interview Design
An interview-about-events protocol was used, where participants interacted with a sensory exercise and conducted four experiments in a laboratory setting as shown in Figure 1.30,34,42 The sensory exercise was composed of two beakers, one containing hot water and the other cold water. This exercise allowed study participants to become comfortable making observations and describing their reasoning. Participants were asked to touch the outside of each beaker and to describe how it felt. They were subsequently prompted to explain their observation by asking “why does it feel that way?” These four particular experiments for the interview protocol were purposefully designed and selected. First, each experiment has a readily observable temperature change. Second, the three chemical reactions represented types of reactions that the students might have seen in laboratory, such as the reaction of HCl(aq) and NaOH(aq), or they represented common classifications of reactions that students would have been exposed to in lecture and laboratory, acid−base reactions and redox reactions. Third, we chose to include one experiment during the protocol that was not a typical “reaction”, but rather a dissolution of a salt. The four experiments used in the interview were (1) the exothermic reaction of 1.0 M aqueous solutions of hydrochloric acid and sodium hydroxide (50 mL each), (2) the exothermic reaction of 50 mL of 1.0 M aqueous hydrochloric acid and a small magnesium strip (ca. 0.12 g), (3) the endothermic reaction of 50 mL of 1.0 M aqueous hydrochloric acid and solid sodium bicarbonate (ca. 4 g), and (4) the endothermic dissolution of ca. 4 g of ammonium nitrate in 50 mL of deionized water. Participants were asked to mix each set of reagents, make observations, collect temperature measurements, and discuss what happened and why. Pencil and paper were provided for students to write or draw anything that would help in their descriptions and explanations.
METHODS
Theoretical Frameworks
The theoretical underpinnings for this work are grounded in constructivism, which posits that, as learners, individuals must make sense of their experiences by building and modifying their own knowledge structures.40 Using this framework as a foundation for the design of this study, individual interviews were used as the primary mode of data collection to elicit understanding that is not accessed by surveys or typical means B
DOI: 10.1021/acs.jchemed.7b00874 J. Chem. Educ. XXXX, XXX, XXX−XXX
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Figure 1. Photos of the hot and cold water beaker sensory exercise (left), the materials for the four reactions/processes (middle), and the typical laboratory setting including stir plate, thermometer, gloves, pencil, and paper (right).
undergraduate chemistry students were recruited from their senior seminar course during their final semester prior to graduation, where each had completed their physical chemistry coursework. The graduate students from the physical chemistry division were recruited via e-mail, where each of the participants to respond were PhD candidates in their third year of graduate school. All participants were given pseudonyms to preserve their anonymity as human subjects in the study.
All written materials were collected as artifacts and incorporated into the verbatim transcripts. The interviews were semistructured in nature, where participants’ dialogue primarily guided the discussion, but was supplemented with questions from the interviewer (the first author) using probing (typically “how” and “why”) questions to elicit observations, descriptions, and explanations.43 If participants did not mention thermodynamic terms such as enthalpy, entropy, or free energy, they were prompted to discuss and relate them to the experiment under consideration at that point in the interview. The interview-about-events approach was selected to reveal participants’ knowledge-in-action rather than having them identify and describe abstract concepts without a specific physical context. This was especially important given the abstract nature of energy concepts and thermodynamic driving forces such as enthalpy, entropy, and Gibbs free energy. Each interview was audio recorded and transcribed verbatim. The study design and interview protocol were reviewed and approved by Purdue University’s Institutional Review Board.
Data Analysis
Analysis of the transcribed interviews involved the generation of interpreted narratives and culminated in a thematic analysis.45 Interpreted narratives were crafted for each interview, containing a summary of basic information about the participant and a table with two columns: streamlined descriptions of the interview on the left with the corresponding interview transcript text on the right. In addition to serving as a summary, the left column of the interpreted narrative tables often contained researcher observations or comments typically based on observations from other interviews or deviations from scientifically accepted ideas (guiding these comments were two physical chemistry faculty interview transcripts and descriptions of each event generated by the authors and other research group members). A thematic analysis of the interpreted narratives was conducted in two stages. The first stage involved a content analysis which utilized the ACS Examinations Institute’s general chemistry anchoring concepts content map (ACCM) to identify the concepts that students discussed throughout the interviews, which was supplemented with open coding where necessary.46,47 For example, the most ACCM common codes related to the anchoring concept of energy (e.g., “heat exchange is measured via temperature change” or “heat flow into/out of the system is defined as endothermic/exothermic”). The second stage consisted exclusively of open coding and constant comparison, where the aim was to discover themes that reflected aspects of participants’ reasoning throughout the interview.48 Passages where students presented rationales for their claim were coded, typically excluding instances where they were solely providing definitions. This typically occurred when students answered “how” and “why” questions and/or used language such as “because”, “therefore”, or “and so that means.”
Participants
A stratified purposeful sampling design was used to support the investigation of chemistry students across many levels from introductory undergraduates to PhD candidate graduate students in the physical chemistry division.44 Table 2 details Table 2. Number of Participants by Level of Coursework Number
Course Level
12 3 5 5
General chemistry undergraduate students Organic chemistry undergraduate students Upper-level undergraduate studentsa Physical chemistry PhD candidate graduate students (third year)
a
Graduating seniors who had already completed physical chemistry coursework.
the number of participants among the introductory- and upperlevel undergraduate chemistry student sample, as well as of the physical chemistry graduate students. The general chemistry students enrolled in the study were from major and nonmajor courses. All were interviewed after the thermodynamics unit in their respective courses. The organic chemistry students were recruited from the majors’ organic course, while the upper-level C
DOI: 10.1021/acs.jchemed.7b00874 J. Chem. Educ. XXXX, XXX, XXX−XXX
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Figure 2. Depiction of students’ reasoning about enthalpy, where introductory students can often identify observed changes as endothermic or exothermic, while more advanced students have access to more sophisticated ways of describing the changes they observed.
Ian: I think it is tough to say because I’m sure there’s got to be some energy going both ways. You have got to put energy into breaking bonds and then when the bond breaks you probably have some energy released because of it. ... There’s got to be some energy transfer going both ways in almost all the cases [of bond breaking and forming]. Because I’m sure bond breaking and bond forming is a lot more complex than they describe it in gen chem... I know in biology... when you get into ATP and ADP... and you break [bonds], energy kind of just flies out of them. But if I remember correctly, they usually describe it as you have to put some energy in to break the bonds, you have to put some energy in to form a bond, and then as a result of bonds breaking usually has a release because of the two. Differences in the descriptions of the four experiments were analyzed across participant levels. Perhaps unsurprisingly, introductory-level undergraduate chemistry students displayed less content knowledge, held many alternative conceptions, and struggled to use scientifically normative ideas appropriately. Upper-level undergraduate chemistry students demonstrated deeper content knowledge, but also demonstrated numerous alternative conceptions (some the same as introductory-level students and some new, related to more advanced content). Finally, graduate-level participants displayed monitoring behaviors as they would correct their incongruent statements during the interview process. Analysis of student reasoning revealed distinct patterns across content topics and student level. The most common content reasoning patterns related to three thermodynamic state functions: enthalpy, entropy, and Gibbs free energy (and spontaneity). Another common introductory-level reasoning pattern was to claim that a chemical reaction occurred when a temperature change was observed. Thus, the fourth experiment, the endothermic dissolution of ammonium nitrate presented a conundrum to these students who struggled to support their explanation through the formation of a putative new substance. Additionally, the most common mode of reasoning that introductory- and upper-level undergraduate students utilized was anthropomorphic (having human characteristics) and teleological (relating to design or purpose) reasoning. The introductory-level students often used these modes of reasoning because they lacked the content background to explain causality for chemical phenomena in a scientifically
Common reasoning pattern codes emerged from this analysis, such as “teleological/anthropomorphic reasoning” or “temperature change signals that a reaction occurred”. Inter-rater reliability was conducted with another researcher; after coding independently, the two researchers met to discuss their coding and made modifications to the applications of the codes as necessary to reach consensus.49 Minor modifications to the coding of the remaining interviews were made accordingly. The data and codes were then analyzed, comparing participant levels. The reasoning patterns that emerged from the analysis were classified according to Talanquer’s41 student reasoning framework as a specific type of implicit assumption or heuristic as shown in Table 1. Classifying the themes which emerged from the data analysis using this framework provided deeper insight into student reasoning and implications for instruction.
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FINDINGS
The content analysis using the ACCM revealed that students frequently discussed temperature, heat, enthalpy, entropy, Gibbs free energy, and spontaneity.47 Common alternative conceptions which emerged during the analysis were related to the energetic nature of chemical bonding, temperature changes associated with chemical reactions, entropy, Gibbs free energy, and spontaneity. For example, participants often described bond breaking as a process which released energy and bond formation as a process that absorbed energy (which is diametrically opposed to the descriptions of bond breaking and formation energetics described in the ACCM). Ian, an introductory-level student, expressed this view and reflected on the source of conceptual confusion, citing bond energy ideas from both chemistry and biology courses. D
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demonstrated that students at all levels reason about entropy as chaos, randomness, or disorder when describing entropy change for a given reaction or process. As shown in Figure 3,
accepted manner. Each of these student reasoning themes are expanded upon in the following subsections. Enthalpy
Analysis across groups of participants from introductory-level undergraduates to upper-level undergraduates to graduate students revealed an ability to reason about enthalpy with an increasing number of modes as shown in Figure 2. For example, introductory-level students were often able to identify the outcomes of experiments as endothermic or exothermic on the basis of observed temperature changes, a mode that aligns with Talanquer’s one-reason decision-making heuristic.41 Ezra, an introductory-level student, demonstrated this when discussing the exothermic reaction of HCl with NaOH. Ezra: After we added the hydrochloric acid to the sodium hydroxide, the temperature increased, of the mixture of the solution. And so that means that the reaction of hydrochloric acid and sodium hydroxide is an exothermic reaction. In addition to demonstrating this mode of reasoning, some students also reasoned that bond breaking and bond formation led to an observed energy flow. This mode reveals that students were utilizing an implicit inheritance assumption. Other students reasoned further by considering relative energies of reactants and products, which led to the observed energetic nature of the reaction or process. When considering the observed temperature increase during the exothermic reaction of HCl and NaOH, an upper-level student, Nate, described that the energy was released because of a change in relative energies from the reactants to the products. During this discussion, he even drew a possible reaction coordinate diagram, labeling the relative energy difference as the amount of energy that was released during the reaction. Nate: It probably went to an energetically more favorable state, or lower. So, this is probably reactants and products. [drew reaction coordinate diagram]
Figure 3. Description of students’ reasoning about entropy, where students across all levels utilized macroscopic criteria as a basis for reasoning.
many participants went beyond this general one-reason decision-making pattern using two specific macroscopic criteria wherein they considered the ratio of reactants to products and/ or the change in states of matter (solid, liquid, or gas). If students utilized both macroscopic criteria and this reasoning produced divergent answers, they prioritized which one was more important, an action that is consistent with the onereason decision-making heuristic.41 Garrett, a graduate student, considered the entropy change for the exothermic reaction of HCl with Mg by considering the change in state. Garrett: I would say the entropy probably increased because we went from a solid to a something dissolved in a solution, so that right there was a pretty visible decrease in order I suppose. Spontaneity and Gibbs Free Energy
Analysis of student reasoning related to spontaneity and Gibbs free energy revealed that students replaced their intuitive ideas about spontaneity with more scientifically complex explanations from introductory-level undergraduates to upper-level undergraduates to graduate students. Introductory-level undergraduate participants often expressed a colloquial understanding of spontaneity (a recognition heuristic), stating that spontaneous reactions/processes proceed without additional energetic input. Most upper-level students conflated their understanding of enthalpy with spontaneity and Gibbs free energy (a representativeness heuristic) with little consideration of entropy. For example, an upper-level student, Mona, demonstrated this, equating exothermic to spontaneous and endothermic with nonspontaneous. The quote below reveals her reasoning about the Gibbs free energy change in the exothermic reaction of aqueous HCl with solid Mg. Mona: It is going to be a negative result as well because it was an exothermic reaction. So, there was energy that was given off, so we did not need any energy from outside anywhere. Interviewer: So, if something is exothermic, is it always going to have like a negative delta G? Mona: I’m sure there is like some special cases, but typically that is how I associate one with the other... We did not have to do any extra work outside of it, like stirring it, or increase temperature for it, or anything like that. Many advanced students expressed a third type of reasoning, where spontaneity and Gibbs free energy were a “balance” of
Yeah, and just, the reactants were at higher energy than the products, so this was the transition. Interviewer: So, it went from higher energy reactants to lower energy products. And so, the energy that we observed being released is kind of like? Nate: This, this difference. [drew arrow and labeled ΔE, denoting the relative energy drop from reactants to products] Figure 2 depicts these three modes as nested boxes, where more novice-like students generally utilize the reasoning mode in the largest box and more advanced students have access to all modes when crafting explanations of their observations. For example, introductory students typically only reasoned about enthalpy by identifying endothermic/exothermic labels based on observed temperature changes. This contrasts with the more advanced students who often exhibited this mode of reasoning, as well as other more sophisticated modes of reasoning, such as the consideration of relative energies of reactants and products. Entropy
Analysis of reasoning patterns pertaining to entropy revealed that the students’ ability to express a scientifically accepted definition of entropy did not vary by level. Analysis of the data E
DOI: 10.1021/acs.jchemed.7b00874 J. Chem. Educ. XXXX, XXX, XXX−XXX
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Figure 4. Development of students’ reasoning about Gibbs free energy, where introductory students often express an intuitive understanding of spontaneity (distinct from Gibbs free energy) and later replace this understanding as they advance in their coursework.
Caleb: It is endothermic because the temperature is going down, because it is stealing heat to start the reaction. I mean it also could be just that this is soluble in water too. I guess I do not know how to tell when it is soluble and when it is actually reacting, but I would assume it is reacting because it is a temperature change. If there was... no temperature change, and they [the solid] all disappeared, I would assume that it is being soluble because nothing is being broken or remade, it is just the polarities [dipoles of the water molecules] line up [to associate with the dissociated ions].
enthalpic and entropic contributions, anchored with the mathematical definition. The quote below from a graduate student, Travis, provides an example of this type of discussion. Travis: Well I mean you know the rule you learn is if delta G is negative then it will happen spontaneously. And if delta G is positive, it will not. ... If you just kind of look at this equation here, ... [points to written work]
Anthropomorphic and Teleological Reasoning
As described in the discussion above regarding participants’ reasoning about Gibbs free energy and spontaneity, our analysis revealed that introductory-level undergraduates often did not possess the resources to consider causality in a scientifically accepted manner. This led them to generate explanations with little explanatory power using anthropomorphic or teleological means. Anthropomorphism is the attribution of human traits (e.g., feelings or desires) to nonhuman entities, whereas teleology is ascribing goals, purpose, or function to phenomena.50 Introductory-level students often described ions, atoms, and/or molecules as intentional agents, implicitly assuming particles behave with purposeful action. Gabriel, an introductory student, used this type of reasoning as he discussed the reaction of solutions of hydrochloric acid and sodium hydroxide. Interviewer: If you had to try to explain why this reaction occurred, how would you go about doing that? What’s the reason it happened? Gabriel: I’d say it is because the molecules preferred to be in these states rather than those states. Or the atoms of the molecules prefer to be in those [product] configurations as opposed to those [reactant] configurations, so when they met up, they split apart and rejoined as a new configuration. Upper-level students also demonstrated this mode of reasoning, but in more subtle ways. Consider Nate’s discussion of why the reaction between solutions of hydrochloric acid and sodium hydroxide occurred. Nate: Why this reaction occurred? Ah. All I know is things like to go to a lower energy state and since the products offered a way for this to go to a lower energy state, it did, even though it probably took some energy to get there. But the end paid off more... It is like an investment. Here, Nate did not use language as strong as “wants” or “prefers”; rather, he reasoned that molecules had knowledge or foresight of the final, lower energy state because they “like to go” to it. He ascribed goals to the final products of a reaction (liking “to go to a lower energy state”), which is an example of using teleological reasoning.
... we see that there is a lower energy in the end than there was in the beginning. And, of course, that is when everyone thinks it would automatically be spontaneous, but that is not true. ... If you had a reaction where... entropy actually decreased, then that works the opposite way as far as spontaneity. So, the more the delta H is negative, the more this quantity [delta G] is likely to be negative, and so yeah, it is looking more and more spontaneous. But if there is some massive decrease in entropy that was large enough in magnitude to offset that and delta G was positive, then it would not be spontaneous. So, things like to be at low energy and high levels of disorder. And in the event that those line up like they do here, then it is going to be spontaneous... Yeah so if these were both negative or both positive, then it could go either way. But if this [delta H] is positive and this [delta S] is negative, then this [delta G] would for sure be positive, and it would for sure not be spontaneous. Figure 4 illustrates a possible Gibbs free energy learning trajectory that emerged from this data analysis, where the data suggest that students modify and replace their modes of reasoning regarding Gibbs free energy from introductory to advanced levels. Temperature Change Indicates Chemical Reaction
Many introductory-level students claimed that an observed temperature change during an experiment indicated that a chemical reaction had spontaneously occurred. Although this reasoning was fruitful during experiments 1−3, it proved untenable during the fourth experiment in the interview
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protocol, the dissolution of ammonium nitrate. Introductory-
LIMITATIONS This study was designed with a stratified sampling technique that allowed us to describe how energy concepts develop across
level student, Caleb, discussed this very idea in the example below. F
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A key finding from this study is that introductory-level students typically do not have the appropriate content background to consider causality in a scientifically accepted manner, leading them to use anthropomorphic and teleological explanations. These findings align with other work regarding student reasoning about mechanism and causality, such as recent studies from Talanquer.63,64 Using energy as a core disciplinary idea to support student understanding throughout the chemistry curriculum is critical to fostering students’ ability to reason about mechanism and causality. 64 Further, thermodynamics concepts, such as Gibbs free energy, should be introduced earlier in the general chemistry curriculum and used across the course sequence to provide students the tools to reason with greater explanatory power and support scientific understanding. Perhaps the most important classroom implication of this study is that instruction and assessment should target student reasoning. The findings of this study demonstrate that anthropomorphic and teleological reasoning were commonplace among the undergraduate participants, even those who displayed correct understanding of thermodynamic concepts. Talanquer posits that such reasoning is appealing because it invokes a desire to attain a more desirable or stable state as the driving force for processes.65 This centralized casual process schema is more comprehensible and provides simplistic explanations for phenomena, making it highly attractive to students.66 Similarly, the use of other implicit assumptions or heuristics, like one-reason decision making, is highly appealing to students, as our findings support. Use of these reasoning modes is not negative in and of itself. For example, the graduate student participants occasionally used these heuristics (affording a shortcut to their answer), but were typically also able to provide scientifically sound reasoning when probed to do so. Therefore, explicit scaffolding and assessment of student reasoning about chemical phenomena is well warranted. Students require assistance recognizing the assumptions and heuristics they use; additionally, they need assistance developing the skills to evaluate the validity of their arguments.41 Assessing student reasoning, through both formative and summative means, is also crucial because assessment is a driving factor in student learning.67−70 We recommend that assessments not only target content mastery, the tiny conceptual bits of knowledge which make up the field of chemistry, but also evaluate reasoning, argumentation, and metacognitive ability. Faculty must elicit student reasoning during instruction and on assessments to guide students to more scientifically correct and useful understandings.
undergraduate and graduate students as they advanced through the curriculum. Essentially this design is a proxy for a longitudinal study. Thus, future work could focus on following individual students across their undergraduate curriculum to document how energy concepts are developed and applied to chemical systems. Additionally, the study was conducted using participants from a single institution. A similar research study conducted across multiple institutions could use the interviewabout-events protocol in different ways and expand upon the findings of the current study.
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CONCLUSIONS AND IMPLICATIONS Findings from this study serve as an important reminder for faculty: chemistry students are learning and exploring chemistry content in other courses, such as biology.16 Energy is not only a disciplinary core idea, but also a cross-cutting concept that students explore and learn about in other disciplinary contexts.2 As students try to build coherent and useful knowledge structures of cross-cutting concepts, they may realize that the description of a concept seemingly varies from one course to another, creating confusion. Participants in this study demonstrated confusion with chemistry concepts because, as Ian demonstrated in his quote, cross-cutting concepts, such as the energetics of bond formation and bond breaking, are discussed differently across science and engineering disciplines. Researchers in chemistry, biology, and physics have begun to study student understanding of cross-cutting concepts across disciplines, an issue called interdisciplinary reconciliation.16,26,35,37,51−57 On the basis of our findings we recommend that instructors address these varying descriptions and applications of cross-cutting concepts explicitly in their classrooms to foster deep, accurate understandings that transcend disciplinary boundaries. For example, using active learning strategies to elicit prior knowledge about energy (or other cross-cutting concepts) is an important step for instructors to tailor instruction that fosters conceptual change and promotes deep, transferable understanding.58 Analysis of student reasoning revealed evidence of potential pathways of learning energy concepts as represented in Figures 2−4. Awareness of these trajectories has implications for instruction, as well as curricular reform. For example, general and physical chemistry instructors should leverage the intuitive understanding of spontaneity that many participants expressed to help guide students to a more sophisticated mode of reasoning seen among the more advanced participants in this study, where they reasoned about spontaneity and Gibbs free energy as a balance of enthalpic and entropic forces. Targeting this partially correct prior understanding and using it productively may allow many students to bypass the middle stage of Figure 4 where enthalpy and Gibbs free energy are conflated. Findings from this research may serve as inspiration to utilize DBER to inform teaching practice. CER, as well as other DBER communities, has large bodies of scholarship that seek to investigate many facets of teaching and learning including how students learn, how to scaffold student learning, how to facilitate conceptual change, and how to measure student learning. One example related to the findings of this study would be that instructors could utilize instruments such as the Thermodynamics Diagnostic Instrument (THEDI), the Thermodynamics Concept Inventory (TCI), or the Thermal and Transport Concept Inventory (TTCI) as effective formative or summative assessment tools.59−62
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Kinsey Bain: 0000-0003-0898-1862 Marcy H. Towns: 0000-0002-8422-4874 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors acknowledge Hayden Hamby, Tucker McCord, Carly Schnoebelen, and Ryan Bain for their assistance on this project. G
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DOI: 10.1021/acs.jchemed.7b00874 J. Chem. Educ. XXXX, XXX, XXX−XXX
