First_DL_activities

First_DL_activities - DL Activity 1.1.1 Getting Started...

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Unformatted text preview: DL Activity 1.1.1 Getting Started with Making Sense of Thermal Phenomena Part A: A Strange Phenomenon—“freezing” a Heatpack As a group trigger one of the heat packs at your table and observe what it does during the first few minutes after triggering. You have a lot of everyday experience with freezing and melting of substances. which is the basis of your intuition about freezing and melting. For example. what does your intuition tell you about what you must do to freeze something? Did the heat pack freeze when triggered? Does this contradict your intuition about freezing? Write some of your groups' responses on the board. Whole Class Discussion Part B: Going back to some basics Before you can make sense of the process that occurs when the heat pack is triggered. we need to review some basics. What we refer to as the Three Phase Model of Pure Substances is a summary of what most of you have seen previously in physical science and chemistry classes with regard to phase changes in ordinary matter. This model of phase changes pretty much fits our intuition. Ourjob now is going to be to make our intuition more precise and reliable. Then we will tackle the job of reconciling our intuitive knowledge of phase changes with the strange behavior of the heat pack. Overview Of the remainder of this activity: You are going to observe a simple phenomenon involving the boiling of water. discuss and establish data patterns and trends, and then relate data trends to a common graphical representation of the Three Phase Model of Pure Substances. 11): Making our intuitive knowledge about phase changes more precise Briefly discuss the following question with your small group (SG) members: Does the temperature of liquid water always increase when it is heated? Think about what your intuition tells you? Does your answer depend on assumptions you are making, perhaps unconsciously about the initial temperature of the water? Write your group‘s response on the board to the question “Does the temperature of liquid water always increase when it is heated?" 12): Observing the phenomenon: Boiling water {~10 min.[ In this part of the activity you will use an electric hotpot and two thermometers to measure the temperature of liquid water as it is heated at a constant rate from the electrical heater embedded in the hotpot. Fill the hotpot about two—thirds with bottled water. Keep the lid on the hotpot while heating to insure a more uniform temperature throughout the water. Use the maximum setting on the hotpot to prevent it from turning off prematurely. (Don’t forget to turn it off and unplug it when you are finished.) Use both of the thermometers you have at your table in order to get a sense of the variability of the temperature readings due to both the limited accuracy of these thermometers and the variation of the temperature of the liquid and water vapor within the hot pot. Continued on side two DL Activit 1.1.1 ' Observe and record the time and temperature at roughly one—minute intervals from the time the water is at about 70 °C until several minutes after it has reached boiling. (Round off reported temperatures to the nearest degree.) ' After the water has been boiling vigorously for a few minutes, measure the temperature of the water vaporjust above the surface of the water. (Simply tilt one thermometer up so its tip is above the water. Keep the lid tightly on the hot pot while you do this.) ' On the board. record in neat columns the temperatures and times that you measure so that other groups can see your results. All members ofyour group must now go to the board and work on the following together. Discuss and write: a) What is the ('otnposition of the bubbles you observe when the water is boiling vigorously? b) Is the temperature of the H10 increased as it changes from liquid to gas? (What did your measurements tell you about the temperature of the water vapor?) c) Do the observed temperatures of the water make sense to you? That is. do they agree with what your intuition says what should happen? d) Think about your answers to (a) and (b) and explain how it is possible to heat a substance and not change its temperature. Whole Class Discussion (3) Using the Three Phase Model of Pure Substances (10-15 mins.) All members of your group must now go to the board and work on the following together. 3) Refer to the back of your Textbook at the Summary of the constructs and relationships of the Three Phase Model of Pure Substances and sketch a complete Temperature v. Energy Added diagram for H30. Clearly label points corresponding to the initial state and thefinal state of the interval you recorded data for in Part 82 b) The overall interval you represented on the Temperature v. Energy Added diagram can be divided into two shorter intervals. Look at your diagram and choose the most obvious place to divide the overall process into two shorter intervals. Indicate this on your diagram by labeling points corresponding to the initial and final states of each shorter interval. What is the relationship between the final values of the state properties (temperature and phase) of the first interval, and the initial values of the state properties (temperature and phase) of the second interval? Think and Discuss You do not have to write anything on the board, but be ready to report your response to the following question to the whole class. c) When two phases of a substance are present and in thermal equilibrium, what do you know with certainty about certain properties or physical conditions as they relate to that substance? Whole Class Discussion DL Activity 1 .1 .2 Analyzing a Heat Pack using the Three Phase Model of Pure Substances Phenomenon: Heat Pack Overview: Observe and begin to make sense of various phenomena associated with a heat pack. Part A: Observe and discuss 15-10 mins.) 1) In order to analyze the strange behavior of the heat pack it is necessary to describe its behavior using the language of the appropriate model. The constructs of the model limit the aspects of the phenomenon that you must pay attention to. Using only the constructs of the Three Phase Model of Pure Substances. what macroscopic properties of the heat pack changed (and how did they change) during the first few minutes after triggering? Write this on the board. [You will continue your analysis of the heat pack in today’s homework assignment.] 2) How does the amount ofenergy associated with clicking the small disk inside the heat pack compare to the other energy transfers that occur. e.g.. the amount of heat transferer from the heat pack to your hands or to the environment? (about the same? much larger? much smaller?) Write this on the board. Whole Class Discussion Part B: Observe and discuss t~10 mins.) Now take the heat pack you triggered through the rest of its cycle. i.e.. get it back to a being a liquid at room temperature (read what it says on the heat pack). Describe qualitatively and briefly how the properties ofthe pack identified in (Al) changed during the rest of the cycle. Write this on the board. Whole Class Discussion Part C: Thinking about the model 15-10 mins.) 1) Think about your response to question (Part B 3c) in Activity 1.1.]. When your heat pack is in a mixed solid/liquid state. what do you know about its temperature? Determine the melting—point temperature of the heat pack. In order to insure equilibrium conditions, you can minimize energy transfers to or from the heat pack by using plastic bubble—wrap to wrap around the heat pack and thermometer. You can also fold your heat pack around the end of the thermometer. Record your result on the board. 2) Two processes that you can readily observe with the heat pack are: i) changing from liquid to solid and ii) changing from solid to liquid. a) For which of these two processes does the heat pack seem to follow the Three Phase Model of Pure Substances and for which does it not follow the model? Be brief, but specific. Put your response on the board. b) For which of these two processes does the heat pack behavior pretty much agree with your intuition about phase changes? For which does it not agree? Put your response on the board. Whole Class Discussion DL Activity 1.1.3 Thinking in terms of Both the Three Phase Model and the Energy- . Interaction Model Overview: Represent, using both the Three Phase Model and the Energy-Interaction Model. several physical processes. All members ofyour group must now go to the board and work on thejollowing together. Your DL instructor will assign one or more of the following processes for your small group (SG) to put on the board, and subsequently explain to the whole class (WC). For each of the physical processes listed below sketch the following: 1) a complete Temperature v. Energy Added diagram with the initial and final states clearly indicated; and 2) an open energy—system diagram. (Refer to the section beginning on page 24 of your Textbook. “General Process of Constructing an Energy-System Diagram") Don‘t forget to include algebraic expressions of energy conservation as a part of your energy-system diagram. 3) Cooling a piece of solid copper (Cu) from 500 CC to 350 CC. b) Warming a piece of ice from —2() CC to the melting point. c) Condensing steam completely to liquid at 100 0C. d) Completely sublimating a chunk ofdry ice at ~79 0C. e) Partially melting 25% of ice initially at 0 OC. f) Heating a piece of copper initially at 300 0C until it is half melted. g) Cooling and completely freezing H30 initially at 80°C. Whole Class Discussion ...
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First_DL_activities - DL Activity 1.1.1 Getting Started...

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