Monday, July 30, 2012

#ModChem Day 12

Modeler's Log, Day 12--

A major endeavor of the modeling methodology of science instruction is to address and correct student misconceptions about science ideas. On day 8, we read an extensive article by Vanessa Barker about the variety of misconceptions that students have about chemistry. We continued today in the direction of misconceptions but narrowing our focus to students' ideas about energy.

William Galley's article "Exothermic Bond Breaking" chronicles persistent misconceptions of energetics by students in a variety of science classroom settings. Galley points to misrepresentation by science textbooks and ineffective instructional practices as being sources of the disinformation that "energy is released when chemical bonds are broken." This leads to what we fondly called the 'Pixie Stick Model' of energy, which many students are led to hold based on instruction in high school biology (and sometimes chemistry) courses. This misconceived understanding of energy views chemical bonds, such as those in the "high-energy phosphate bonds of ATP," like Pixie Sticks. When the Pixie Stick bond is "broken," the energy is "released" like the crystals inside of the Pixie Stick. It is misleading to students that bonds are talked about as physical objects that can "contain" energy, when it actually is the case that the bond is not a physical object but rather an interaction between electric fields, where the energy is really stored.

We noted from the article that traditional language used to describe chemical bonds, especially the language associated with energy molecules in biology courses, can be attributed to this inaccurate view. We all agreed that we cannot use language that makes it seem like bonds "store energy" or that "energy is liberated upon cleaving the high-energy bonds of ATP" in biology courses, but also that we need to be cognizant of these preconceptions when students enter high school chemistry courses.

Instead, we must do a better instructional job of helping students to realize that it takes energy to break bonds and can release energy when bonds are created. In the end, there really needs to be a comprehensive model that takes into account both bond making, bond breaking, and the net energy transfer after a chemical reaction is completed. Focusing on energy transfer in chemical reactions proves, according to Galley's article and the Modeling Instruction research, far more useful in communicating a coherent view of energy. Galley also promotes schematic diagrams to represent the energy transfer in systems, which he describes happens more frequently in college-level chemistry courses. Other recommendations from Galley include, teaching the difference in bond energy between substances more explicitly, as well as better communicating that the bond energy refers to energy required to break a bond. These changes can make clear that it takes energy to break bonds and releases energy to make bonds; therefore, it's the net energy that really determines the exothermic vs. endothermic descriptor of a chemical reaction.

Following the conclusion of our article discussion, we practiced whiteboard questioning with balancing chemical equations and representing the balanced reactions with particle diagrams. There are several strategies out there to balance chemical equations, but often it is taught in a way that makes it seem like there are procedural rules that can be algorithmically followed--that isn't always the case. What is the case is that some methods of balancing chemical equations, especially those that do not include particle diagrams, can lead students away from having a concrete conception of what is physically happening in a reaction. All balancing strategies taught in modeling chemistry are accompanied by a particle diagram. This provides a visual basis for self-assessing the correctness of the balanced chemical equation.
Since the modeling method stresses the importance of having a particle view of matter, the diagrams become imperative in balancing reactions. This also keeps students grounded in the model of chemical change that is 'rearrangement of atoms' and thus conservation of matter.

Our questioning has improved, but one thing that we all noticed in each other was how much we gravitated toward positive feedback in playing the role of teacher questioning students. We all have been encouraged to maintain a good level of praise in the classroom, but it was noted that the object of the praise became unclear to students in some situations and could lead to a false sense of confidence in one's problem-solving strategy. In our debrief, this led to the question of praise in the classroom (2012) and its role in whiteboard questioning sessions. How/when to praise? An interesting technique called, "Right is Right," was brought up from Doug Lemov's Teach Like a Champion book. According to this technique, it is important to hold content/strategy praise until a right answer is presented. Attempting to praise an attempt or effort when a response is inaccurate can mislead students into believing their thinking is sound.

The praise discussion poured over into a discussion of the classroom climate that would encourage risk-taking and a sense of security. We kept coming back to a notion we arrived at earlier in the course, 'modeling doesn't work if you don't build relationships.' This mantra is essential in making a successful modeling classroom and modeling instruction experience for students. There are many different strategies for building rapport in ones classroom, but everyone must do something that fits their personality and teaching style. Instruction must be personalized and the human element cannot be omitted if you want your class to be a success.


Next up was a set of reaction lab stations, where students have the chance to observe many different types of reactions and determine the physical signs that a chemical reaction has taken place. By comparing and contrasting the different reaction types they observe, the lab stations can elucidate patterns in chemical reactions to students and give rise to a predictive model for determining products. This takes students into classifying and modeling with equations the different types of reactions.

I recalled how I used to teach reaction types, as I was shown to do in my student teaching, which was to model the reaction equation templates as relationships between people. For example, my mentor teacher suggested that a double replacement reaction was just like the TV show Wife Swap. Instead of writing out AB + CD --> AD + BC, I used to draw out stick figure couples of husbands and wives, then show the swapped couples! Though it was laughable and memorable, it didn't really make clear anything chemical about the reactions for most students. When I discussed this former approach with my fellow workshop participants, we decided that was poor practice because it personified chemistry. Be careful with 'personifying elements' to students; though it might be memorable in a story-like way, it can tend to oversimplify, or even mislead students about, the concepts.
I am still entertained, however, with this personification of elements and reactions by the Marie Curie Fellowship. Just for fun, here it is:


Finally on the day, we took our balanced equations and looked for a way to represent energy in reactions. Based on our Galley article reading, and inspired by our previous treatment of energy from day 6, we chose to follow our established conventions in the LOL diagrams to represent chemical energy transfer. We brainstormed how we could characterize the difference between exothermic and endothermic reactions in sequence with our modeling curriculum, and we concluded that we could introduce endothermic v. exothermic v. activation energy based on energy transfers and overall net energy transfer during reactions. Chemical reactions trasnfer energy "internally" within the system, but can ultimately translate to a transfer of energy into/out of the system through heating. We agreed to describe endothermic reactions as products require more energy than reactants to maintain their particle arrangement and exothermic reactions as products require less energy than reactants to maintain their particle arrangement. This allows students to fit the terminology into their model of energy transfer.

With this approach, it is important to focus on keeping separate the internal energy transfer between energy "accounts," how the system is defined, and how energy can be transferred into or out of the system from/to the surroundings. Depending on your course curriculum, we found this to be an appropriate place to introduce spontaneity in reactions and discuss when energy transfer occurs. During spontaneous processes, the energy transfer with the surroundings occurs after the reaction; however, during non-spontaneous processes, the energy transfer with the surroundings occurs before the reaction in order to make it happen. Including activation energy can be done here, but it should be incorporated in a manner consistent with the LOL diagrams model of energy transfer; otherwise, it can be held off until a study of reaction kinetics.

The modeling approach to representing energy transfer is inspired by the work of Gregg Swackhamer, but is presented in an insightful manner by Larry Dukerich, here in this approach to representing energy transfer with chemical reactions:





2 comments:

  1. The different media embedded really help to complete the reader's understanding of your text!

    ReplyDelete
  2. I liked the point about what is missing in the learning process. Really made me think.

    ReplyDelete