Lesson Plan: Modeling the Melting of Ice FOR THE TEACHER Summary In this lesson, students will create a particulate model of matter that explains energy changes and transfer during a phase change. Grade Level Middle and High School
Submitted by ACS High School Professional Development Team Washington, D.C.
NGSS Standards •
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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).
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Science & Engineering Practices o Developing and using models o Constructing explanations (for science) and designing solutions (for engineering) o Engaging in argument from evidence
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Crosscutting Concepts o Cause and effect: Mechanism and explanation o Systems and system models o Energy and matter: Flows, cycles, and conservation
Objectives By the end of this lesson, students should be able to • Use the particulate model of matter to explain phase change processes based on changes in the kinetic and potential energy of the particles that make up a system. • Represent changes in the energy of a system during a physical process using graphical representations. Chemistry Topics This lesson supports students’ understanding of • Phase Changes • Kinetic Energy • Potential Energy • Temperature • Heat Time Teacher Preparation: 20 minutes Lesson: 120-180 minutes, depending on application.
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Materials • Amazing Ice Melting Blocks 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. • Two Ice Cubes per Group • Paper Towels • Handheld IR thermometer Safety • Always wear safety goggles when handling chemicals in the lab. • Students should wash their hands thoroughly before leaving the lab. • Follow the teacher’s instructions for cleanup and disposal of materials. Teacher Notes • Course Sequence Suggestions: This lesson was originally designed to follow a lesson on particulate energy transfer. Click here to view the previous lesson. •
Describing matter on the particle level: Use Modeling Energy Transfer as well as this lesson to establish particle-level conceptions of energy immediately after establishing particle-level conceptions of matter. Modeling matter provides a natural transition to modeling energy. Students may ask (or you may prompt) questions like ‘What is the difference between hot and cold water at the particle level?’ Establishing particle-level energy conceptions early allows for those conceptions (and energy in general) to be woven into the classroom more often and more effectively. You may wish to skip the bar graph modeling initially and revisit the phenomenon later in the year, possibly when the study of energy becomes more quantitative. This not only limits the time required, but allows for the iterative nature of modeling to take place.
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Energy in phase changes: This lesson may be used within a more traditional energy unit, such as in exploring energy associated with phase changes (ex. Heat of fusion) or establishing conservation of energy. This lesson will help develop a particle-level conception as well as begin a more quantitative discussion of energy. During the energy bar graph portion of the activity students may ask (or you may prompt) questions like ‘How could we more exactly quantify how much kinetic energy an object possesses?’ or later on ‘Imagine you have two samples of a substance. They’re both at the same temperature, but one is twice the mass of the other. How does the kinetic energy of the two objects compare?’ These conversations lead to a need for quantitative ideas like specific heat and heats of fusion/vaporization. While developing a quantitative understanding of these ideas, you may wish to revisit the energy bar graphs. Have students draw approximate energy bar graphs for a scenario (Ex. Liquid water at 20oC being cooled to -5oC) and then build quantitative versions with correct scales and values for the same scenario (Ex. 10g of water cooling from 20oC to -5oC) using their specific heat and heat of fusion tools.
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Liquids and solids: Why is an investment of energy required for a substance to transition from solid to liquid? Do all substances require the same investment of energy to transition from solid to liquid? Why does this transition occur at different temperatures for different substances? Use this lesson as a starting point for using energy data to explore interparticle attractions and how they may vary between substances.
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For additional background information, refer to the additional background information document available for download. A list of teaching resources is also included.
FOR THE STUDENT Lesson Modeling the Melting of Ice In our exploration of the tiles, we ended with a macroscopic model of thermal energy transfer as well as a model that explained our observations in terms of the movement and interaction between the particles. 1. Now, we will think about the process of the melting of the ice. Using the model that you came up with previously, describe how the particles will be moving in the ice as kinetic energy continues to be transferred from the tile to the ice.
2. If the particles are behaving in the way that you have described above, how will the temperature of the ice change as it melts?
3. Test your prediction by measuring the temperature of the ice as it melts using an IR thermometer. Record your observations here.
4. Do your observations support your model? Explain how your observations fit with your model and modify your model to better incorporate any observations that contradict it. Be prepared to share your group’s model with the class.
5. Suppose a piece of ice is taken out of a very cold freezer (-40oC) and placed into a beaker. Then it is placed on a hot plate and heated, transferring energy to the ice at a constant rate. The temperature is taken until the ice has melted. What
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would the graph of Temperature vs Time look like? Make your prediction on the graph provided below.
Your instructor will provide you with a graph of Temperature vs Time. 6. In the circles below, draw particle models for the water at each section of the graph.
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7. Using the model that you developed, what can you say about the kinetic energy of the particles during each portion of the graph? During each portion of the graph, how is the behavior of the particles changing as energy is added?
8. Some of the information from the graph suggests that the added energy does not only change the movement (kinetic energy) of the particles. What other particle changes are being caused by the addition of energy?
9. How do the particles of a substance change during the phase change? What role do you think energy plays in the change?
10. As a group, return to the model of the melting ice from question 1. Modify your model to incorporate any new understandings of the role energy plays in phase changes.
11. Now that we’ve come to a consensus as a class, let’s think about how we can model the changes in energy visually and graphically. a. What objects are exchanging energy in this situation? List the objects that are exchanging energy and connect objects that are exchanging energy with a line.
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b. The diagram on the right (known as a schema) represents some of the key objects in this situation. The dashed circle separates the system (objects we’re studying) from the surroundings (everything else). Draw arrows at the end of each solid line indicating the direction of energy transfer between objects. 12. Use the chart below to represent the initial distribution of energy and how the energy flows at each stage in the process.
A
B
C
D
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13. Now, let’s see if we can apply our model to the reverse process. Consider liquid water being placed into a cold freezer. How will the behavior of the particles change over time? How will energy be exchanged over time? Use the diagrams provided below to construct your model of the process.
Liquid
Freezing
Solid
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