Lesson Plan: What Makes Something Feel Warm? Modeling Energy Transfer: A Macroscopic and Particulate View FOR THE TEACHER Summary In this lesson students actively engage in thinking about energy issues in chemistry and the nature of energy (thermal) transfer. The idea that temperature is a measure of heat content will be challenged, and students will be given the opportunity to collect data that will allow them to clearly see that different materials transfer energy at different rates.
Submitted by ACS High School Professional Development Team Washington, D.C.
Grade Level Middle and High School NGSS Standards • MS-PS1-4: Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed. • MS-PS3-2: Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system. • HS-PS3-2: Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motions of particles (objects) and energy associated with the relative position of particles (objects). Science & Engineering Practices (SEP) • Developing and using models • Constructing explanations (for science) and designing solutions (for engineering) • Engaging in argument from evidence Crosscutting Concepts (CCC) • Cause and effect: Mechanism and explanation • Systems and system models • Energy and matter: Flows, cycles, and conservation Objectives By the end of this lesson, students should be able to • Construct a macroscopic model (based on temperature, density, and thermal conductivity) of how energy is transferred. (For higher level students, specific heat capacity can also be explored.) • Explain how temperature is related to average kinetic energy if using the supplementary “What is Temperature?” demonstration. • Explain how perception of hot or cold is related to heat and temperature. • Use the particulate model of matter to explain how kinetic energy is demonstrated amongst the particles of a substance.
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Chemistry Topics This lesson supports students’ understanding of • Heat • Temperature • Average kinetic energy • Properties of matter • Energy transfer • Thermal conductivity • Density • Specific heat capacity Time Teacher Preparation: 15 minutes for Exploration #1 and 15 minutes for Exploration #2 Lesson: • Exploration #1: 30-45 minutes • Exploration #2: 50 minutes Materials • Power Point Slides • Ice Melting Blocks (like Arbor Scientific Ice Melting Blocks) for each group • IR Thermometers (like Thermoworks IR Pocket Thermometer) for each group • Two Ice Cubes per group • Paper Towels for each group • Student Whiteboards and Markers (or chart paper and markers) for each group Safety • Always wear safety goggles when handling chemicals in the lab. • Students should wash their hands thoroughly before leaving the lab. • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals. Teacher Notes Course Sequence Suggestions This lesson fits well when introducing ideas of energy and heat. It reveals students’ preconceptions about temperature and heat, and challenges the idea that temperature is the measure of how hot or cold something is. Additional Suggestions: • Pre-label the tiles A and B. It is easier for the teacher if all of the polystyrene tiles have the same letter and all of the aluminum tiles have the same letter. • Temperature is not a measure of heat. You can define temperature as the measure of average kinetic energy of the particles during “Step 2 #9 – Share your ideas with a partner. At this stage it is essential that all students are clear that temperature is a measure of average KE, and not a measure of heat. You may want to use the “What is Temperature?” demonstration to help students understand how temperature and average kinetic energy are related. • After completing “Step 5: Explanation” and before starting “Analysis Questions” is a good place to introduce the concept of specific heat capacity if appropriate for your
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students. Please see the “Dramatic Demonstration of Thermal Conductivity” and/or the “Measuring Heat Demonstration” for ideas on how to extend. The activity provides several paths that can: • help students build an understanding that our perception of hot and cold is due to the rate of energy transfer • introduce or reinforce the idea that temperature is a measure of average kinetic energy • introduce the concept of thermal conductivity • guide students to understanding that heat can ONLY be measured when there is a transfer of energy from one thing to another • begin a discussion of heat capacity • facilitate modeling thermal energy transfer on a macroscopic and particulate level • inspire questions about entropic ideas in energy transfer and thermal equilibrium for advanced students A nice application lesson that can follow, is an engineering design activity called “Design a Fast Defroster for the Forgetful Chef”. In the lesson, students are asked to use their knowledge of materials to design a device that will defrost quickly. Background Information for Teachers Although most students have a common sense idea about what energy is, they may find it difficult to give a precise definition. Teaching students about chemical energy can be even more difficult. This may be due in part to the fact that we often postpone discussion of energy until late in the year, when we cover topics such as thermochemistry and thermodynamics; despite the fact that energy is a cross-cutting concept that accompanies every change in chemistry. As Richard Feynman said, “It is important to realize that in physics today, we have no knowledge of what energy is!” Our main experience with energy comes when we recognize energy changes. In this session we will explore changes in thermal energy, such as how we feel when we forget to put on a sweater during cold weather, or when we wear too many clothes when it’s hot outside. Students’ understanding of heat, temperature and chemical systems needs to be carefully constructed. For more background information on these topics, download the Teacher Background Information document. You might also find the opportunity to extend this activity when discussing specific heat. Many students are confused by the idea of specific heat, and think that it is how much heat something can hold. To battle that idea, one must be clear that the definition is the amount of energy needed to change the temperature of a certain amount of a substance. If we think about particles, it is the amount of energy needed to be transferred so that the particles increase their average KE. There are two supplementary demonstrations that provide observations and data for students to build a better understanding of heat capacity. See Please see the “Dramatic Demonstration of Thermal Conductivity” and/or the “Measuring Heat Demonstration”. Student Prerequisite Information • Students should have a particulate view of matter, i.e.: should know that matter consists of small particles. • Students should have experience with measuring temperature and with units of •
temperature.
Students should have a definition of kinetic energy being related to velocity of the particles, i.e. KE=½ mv2
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References: •
Bell, J. (2013): Energy Foundations for High School Chemistry, American Chemical Society. .
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Carl A. Doige & Terence Day (2012): A Typology of Undergraduate Textbook Definitions of ‘Heat’ across Science Disciplines, International Journal of Science Education.
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Hutchinson, John: Concept Development Studies in Chemistry Chapter 12 the Kinetic Molecular Theory and Chapter 17 Equilibrium and the Second Law
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Lasance, C. (2007): Thermal Effusivity, Electronics Cooling. .
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Zemansky, Mark (1970): The Use and Misuse of the Word "Heat" in Physics Teaching, Phys. Teach. 8, 295
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http://highschoolenergy.acs.org/content/hsef/en/energy-theories/cold-doesntexist.html
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Dr. Jack Josefowicz’s explanation on Thermal Effusivity.
FOR THE STUDENT Lesson
Modeling Energy Transfer: A Macroscopic View and Engineering Practices Learning Objectives ● Students will construct a particulate model to explain thermal energy transfer. ● Students will understand the relationship between temperature and thermal transfer. ● Students will explain how perception of hot or cold is related to heat and temperature. ● Students will use the particulate model of matter to explain how kinetic energy is demonstrated amongst the particles of a substance. Warm Up 1. The Sweater: This winter was soooo cold. My mother told me to “put on a sweater, because I’m cold”. Why do mothers tell their kids to put on a sweater? What is it about the sweater that keeps them warm?
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2. The Forgetful Chef has a problem. The chef needs to thaw the chicken as quickly as possible, but doesn’t want to heat it in the microwave or in hot water because it might pre-cook the meat. Below is a list of materials the chef has in his kitchen that he is considering placing the chicken on. Which one do you think might be the best option? Explain your choice. • Wooden Butcher Block • Granite countertop • Aluminum baking pan • Glass bowl • Plastic container with cold water • Kitchen towel
Materials ▪ 2 Black Tiles ▪ IR Thermometer ▪ 2 Ice Cubes ▪ Paper Towels Exploration #1: Observe the Properties of Materials Step 1: Observe each of the tiles. How you can use your senses to make observations. 3. Record your observations.
4. Which tile feels warmer? 5. Based upon your initial idea about the sweater: a. Predict which tile (A or B) has a higher temperature, if either: b. Predict the actual temperature of each tile: Tile A: _____________ Tile B: _____________ American Association of Chemistry Teachers
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Step 2: Test your temperature predictions. Flip the tiles over and use an IR thermometer to test the temperature of each tile. Record the temperatures: Tile A: _____________ Tile B: _____________ 6. Did your prediction match the actual temperatures of each tile? 7. What do you think temperature measures?
8. Try to explain your results. Consider both drawing a picture and writing your ideas about what may be happening.
9. Share your ideas with a partner. Try to come to a consensus about your explanations. Record any new ideas that support your initial explanation about what may be happening.
Step 3: Prediction 10.Suppose you were going to place an ice cube on each tile. Based on your explanation in the previous step, predict which tile (A or B) will melt the ice cube faster, if either. Describe your prediction.
Exploration #2: Observe Ice on Material Step 4: When your teacher indicates, place one ice cube on each tile. Make observations of the ice on each of the tiles. 11.Record your observations.
12.Record the temperature of the tiles, after 2 minutes.
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Tile A: _____________ Tile B: _____________ 13.Individually: a. Summarize the results of all your observations so far in the table below. Tile A
Tile B
Feeling Temperature (before ice) Relative rate of ice melting Temperature (after ice) Other observations: Specify b. Given temperature is a measure of average kinetic energy of the particles. What can you conclude about the average kinetic energy of Tile A and Tile B before the ice was placed on them?
c. What do you think happened to the kinetic energy of the particles in Tile A compared to Tile B after the ice was placed on them?
d. Refine your explanation (about the tiles you made in question 9) in light of these new observations.
Step 5: Explanation Now share your ideas with your group. As a group, think about how the difference in melting time can be explained in terms of the behavior and interaction of the particles that make up the tiles and the ice. The model you develop should explain your observations.
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Use the questions below as a guide for developing your model. Represent your model using a set of particulate drawings that describe the interactions between ice particles and tile particles. A written explanation should be included. ● How do the particles that make up the ice interact with the particles that make
up the tile?
● How does the behavior of the particles that compose the tile change when the
temperature of the tile changes?
● Consider the role that energy plays in your model. How is energy transfer
represented in your model?
Be prepared to share out your models and discuss your group’s ideas with the class. Analysis Questions: 14.Why do you think it was necessary to flip the tile over after feeling the tiles and before measuring the temperature?
For the next two questions, use macroscopic ideas (like temperature, phase change, etc.) to help with your explanations.
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15.Tile A conducts thermal energy better than the tile B. (We call Tile A a thermal conductor) What does it mean to conduct thermal energy? Your explanation can include a written description or well-labeled drawing.
16.A good insulator is the opposite of a conductor. What do you think it means if something is a good insulator? Your explanation can include a written description or well-labeled drawing.
17.Do you think something that feels warm, like the sweater, is a conductor or an insulator? Explain your answer.
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