##
* *Reflection: Developing a Conceptual Understanding
Reflecting on Thermodynamics - Content and Process - Section 3: Kinetic Theory Exercise

I'd like to elaborate on one student's response that I captured on the board. When comparing his solid model to his liquid model, one can see that the lines he drew changed from straight to wavy.

While at the board, I asked him to describe the differences in those lines. He said he used solid lines for strong bonds and wavy lines for weak ones. He also offered that the number of bonds wasn't any different, only the strength of the bonds.

This offered us the opportunity to discuss the true nature of the bonds; the tiny electrical asymmetries of molecules that create inter-molecular forces. Furthermore, it prompted some discussion about the strength of the bonds versus distance, the breaking of some bonds in liquids, followed by the rapid establishment of new bonds with new "neighbors," and the relative difference in the motion of the particles in different states ("slow" in solids, "faster" in liquids, etc.).

This was a little bit of a tricky conversation as students come into this course with a wide variety of backgrounds. These students have a common 8th- and 9th-grade science experience but are allowed to choose science courses from the 10th-grade on. Those students who have had Chemistry are fully prepared to talk about inter-molecular forces while those that haven't are less likely to have a rich understanding of the molecular world. The next unit will bring all students up to a common understanding of electrical forces but, for now, there exists a bit of a gap.

*Developing a Conceptual Understanding: Student Samples*

# Reflecting on Thermodynamics - Content and Process

Lesson 14 of 14

## Objective: Students will look back at this unit on Thermodynamics and self-assess their understandings.

*80 minutes*

Today's lesson is the final lesson of the Thermodynamics unit. Part of the lesson is devoted to transitioning from this unit to the next ("Electrostatics") through the examination of particles on the molecular and atomic scales. In addition, I provide some time for my students to respond to some of the most essential questions of this unit. Students have not been prepared for this set of questions, other than through their day-to-day work. As such, their responses will only be graded for completion.

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#### Warmup

*20 min*

Today's warmup provides students an opportunity to demonstrate their understanding of our recent work in calorimetry. A challenge for teachers, of course, is to vary problems over time to stimulate student thinking and to avoid a sense of "mental inertia" where students reflexively respond to familiar problems. Today's problem is an attempt to create a novel situation where no new knowledge is needed, just an ability to extend previous knowledge.

The problem features more than one object being mixed into a calorimetry water bath. With multiple items being mixed together, students need to extend the concept of energy conservation to be successful. In addition, they are asked to limit their answer to an appropriate number of significant digits. This problem does not demand much new of students but is a good opportunity to see if they can be agile enough to include all the physical elements.

I give the students 4-5 minutes to work on this and, if necessary, supply suggestions for those students who seem stuck. The final discussion of this problem can proceed quickly, once students see the way that each element can be factored into the solution. Indeed, I try NOT to get too deep into the algebraic solution; once I provide the physics set-up (the way in which all four terms are included in the solution), I ask students to provide me with the intermediate calculations and work quickly to the final answer. The value of this problem, at this point in the unit, is overwhelmingly in the first two steps with little to learn beyond that.

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#### Kinetic Theory Exercise

*30 min*

In the previous lesson, we filled out the first page of the Kinetic Theory notes and images. I asked for qualitative language to describe the bonding, spacing, and movements of the molecules in three states of matter. I also probed their understanding of what happens when more energy is added to a substance.

For today's exercise to work it is imperative that I not describe the nature of the bonds. I ask students to illustrate with solids and liquids "what is happening between the molecules." I anticipate they'll draw springs or arrows or links, and that these drawings will look different between the solid and liquid drawings (pages 2 and 3 of the handout). As we move from solids to liquids to gases, I prompt students to think about what happens to their model (say, solids) when more energy is added to the object. In this way, we connect back to the ideas of this unit on thermodynamics.

After illustrating their copy, students share with one another and then share with the class. I have one or two students come to board and draw their models, as a way to appreciate the ways in which the bonds can be considered. After some time, I ask them to adapt their model to gases, based on the bonding, spacing, and movement notes from the first page.

My goal in this segment is to have students access their thinking about the nature of these bonds - and how these bonds are altered with increases in thermal energy - without simply telling them. I think it's important for students to get their models out of their minds and onto paper for sharing and evaluation. After sharing, I think students will be ready to consider the idea of small but vital electric forces that bind molecules together. Those electric forces are, naturally, the result of charges and both electric forces and charges will be the main topic of the next unit.

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#### Reflection on Thermodynamics

*30 min*

As we finish our study of thermodynamics, I look for an opportunity to capture student understanding in a formative setting. I have decided to assess this way, as opposed to the more traditional testing approach, for several reasons. First, I have already collected many samples of summative student work throughout the unit. Second, I value the conceptual understanding at least as much as a computational demonstration of knowledge. Indeed, there have been times when students have been able to perform the calculations without truly understanding the physical principles involved.

To accomplish this, I ask students to address a short set of Thermodynamics Essential Questions, using a Google form for submission. Their responses will be recorded directly into a spreadsheet for me to read and evaluate at another time. Their responses are not graded but provide me with a rich data set to reflect upon the success of the unit. Finally, though the responses are not graded, I do record a small participatory grade for all completed questionnaires, so students provide their names for that purpose.

As a means to alter mood, I reserve time in the library for students to complete this task. In addition to the change of scenery, the library offers a sufficient bank of computers for students to complete this task. Furthermore, I share with my students that this is the final activity for our unit on thermodynamics. We take the remainder of class time to access and complete these questions.

I have provided screenshots of the questions called thermodynamic essential questions part 1 and thermodynamic essential questions part 2. In addition, the entire set of student responses is provided.

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- LESSON 1: Introduction to Physics via Thermodynamics
- LESSON 2: Temperature Slopes and Meaning-Making
- LESSON 3: Determining Heater Ratings Experimentally - Day 1
- LESSON 4: Determining Heater Ratings Experimentally - Day 2
- LESSON 5: Wrapping Up the Immersion Heater Investigation
- LESSON 6: Exploring Calorimetry
- LESSON 7: Conservation of Energy . . . To the Rescue!
- LESSON 8: Enhancing Our Energy Model: From Naive to Sophisticated
- LESSON 9: Testing Our Thermal Loss Procedures
- LESSON 10: Hot Rocks Lab Work - Day 1
- LESSON 11: Hot Rocks Lab Work - Day 2
- LESSON 12: Hot Rocks Lab Work - Day 3
- LESSON 13: Kinetic Theory of Matter
- LESSON 14: Reflecting on Thermodynamics - Content and Process