Phase Changes Gizmo Answer Key

Name: Amara Owen Date: 07-08-2022 Student Exploration: Phase Changes Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: altitude, boil, boiling point, freeze, freezing point, gas, liquid, melt, melting point, phase, solid Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. A family from Minnesota turns off the heat and flies to Florida for a winter holiday. When they come home, all of their water pipes have burst. What do you think happened? The water in the pipe froze and made them burst 2. Spaghetti takes about 9 minutes to cook at sea level, but about 14 minutes in the mountains. Why do you think this is so? There, the water has a lower boiling point, which results in colder water and slower pasta cooking Gizmo Warm-up In the Phase Changes Gizmo, select Micro view and set the Ice volume to 50 cm3. Notice the nitrogen ( ), oxygen ( ), and water ( ) molecules. Click Play ( ) and observe water molecules in the solid (ice), liquid (water), and gas (air) phases. 1. In which phase(s) are the molecules held rigidly together? Solid 2. In which phase(s) do the molecules move freely? Gas and liquid 3. In which phase(s) are the molecules held in a defined shape? Solid and liquid 4. In which phase(s) do the molecules take the shape of their container? Liquid Get the Gizmo ready: Activity A: Phase changes ● Click Reset ( ) and select Macro view. ● Set the Water temperature to 10 °C. ● Set the Ice volume to 0 cm3. Question: How is temperature related to phase changes? 1. Predict: Based on your prior knowledge, predict the following: A. At what temperature will water change from a liquid to a solid (freeze)? 0 B. At what temperature will water change from a solid to a liquid (melt)? 0 C. At what temperature will water change from a liquid to a gas (boil)? 100 2. Investigate: Use the Gizmo to explore phase changes. Use the Add/remove heat energy slider to control the water temperature. Record your observations in your notes, then answer the questions below: A. At what temperature does water freeze? 0 This is the freezing point. B. At what temperature does ice melt? 0 This is the melting point. C. At what temperature does water boil? 10 This is the boiling point. 3. Observe: Set up the Gizmo to observe freezing. What do you notice about the temperature while the water is in the process of freezing? Remains unchanged 4. Explore: Use the Gizmo to investigate melting and boiling. Does the temperature change while either of these phase changes is occurring? No it doesn't 5. Interpret: Select the GRAPH tab to see a graph of temperature vs. time. Click the “–” button until the whole graph is visible. What does the graph look like during a phase change? A horizontal line 6. Extend your thinking: Why do you think the temperature does not change much during a phase change? If possible, discuss your answer with your classmates and teacher. Utilizing the energy to alter the nature of matter Get the Gizmo ready: Activity B: Temperature and molecular motion ● Click Reset, and select the Micro view. ● Set Ice volume to 0 cm3. ● Set Add/remove heat energy to 0 J/s. Question: Why do phase changes occur? 1. Compare: Set the Water temperature to 0 °C and click Play. Observe the water molecules. Click Reset, set the Water temperature to 100 °C, and click Play again. What do you notice? Nothing differs, there is no difference. 2. Observe: Click Reset. The mean molecular speed of the water molecules is displayed below the container. Set the Water temperature to 0 °C and Add/remove heat energy to 400 J/s. Click Play. A. How does the mean speed of the water molecules change as they are heated? Increases the hotter water gets B. Does the mean molecular speed change as much as the temperature as the water heats up? Explain. Yes, as the mean molecular speed varies as temperature rises. 3. Explain: How is temperature related to the motions of molecules? The molecules move more quickly as the temperature rises. 4. Observe: Click Reset. Set the Water temperature to 20 °C and the Ice volume to 50 cm3. Set Add/remove heat energy to 0 J/s. Click Play. How do the molecules in the liquid interact with the molecules in the solid? The bonds are broken when the molecules of the liquid collide with those of the solid. 5. Observe: Click Reset. Set the Water temperature to 100 °C and the Ice volume to 50 cm3. Click Play. How does this situation compare to the previous one? Ice melts more quickly 6. Propose a theory: Based on what you have observed, explain why you think phase changes occur. If possible, discuss your theory with your classmates and teacher. They transform because their link can no longer contain the excess kinetic energy that is present within them. 7. Apply: Use your theory to explain what happens at the molecular level in each of the following situations. Also, list the temperature at which each transition occurs. A. Ice is warmed to the melting point. Atoms are fast enough to break bonds and turn into liquid Temperature: 0 C B. Water is warmed to the boiling point. The atoms move swiftly and get heated enough to turn into vapor. Temperature: 100 C C. Water is cooled to the freezing point. The atoms slow down till they are stable enough to start forming bonds Temperature: 0 C 8. Extend your thinking: Click Reset. Set the Water temperature to 0 °C, the Ice volume to 0 cm3, and Add/remove heat energy to -400 J/s. Click Play and wait until all of the water freezes. A. What volume of ice is created from 200 cm3 of water? B. Why do water pipes sometimes burst in the winter? Water expands as it freezes, causing it to burst. 217 Get the Gizmo ready: Activity C: Altitude and phase changes ● Click Reset. ● Set Ice volume to 0 cm3. ● Set the Altitude to 5,000 meters (16,404 feet). Question: The altitude of a location is its vertical distance above sea level. How does altitude affect phase changes? 1. Form a hypothesis: As altitude increases, the air pressure decreases. How do you think the lower pressure will affect the following? (Highlight your answers. ) A. Freezing point: Increase Stay the same Decrease B. Melting point: Increase Stay the same Decrease C. Boiling point: Increase Stay the same Decrease 2. Experiment: Use the Gizmo to find the freezing, melting, and boiling points of water at 5,000 meters (16,404 feet). Write these values below. Freezing point: 0 Melting point: 0 Boiling point: 83 3. Analyze: How did altitude affect the freezing, melting, and boiling points of water? Boiling point dropped, while freezing and melting points remained unchanged. 4. Challenge: Try to explain these results based on the fact that air pressure decreases with altitude. If possible, discuss your ideas with your classmates and teacher. Because there is less pressure on it, breaking the bonds requires less kinetic energy when there is less air pressure. 5. Apply: Why does pasta take longer to cook in the mountains? The pasta cooks more slowly because the water can't reach a high enough temperature. 6. Apply: A pressure cooker allows food to be cooked under high pressure. Why is this useful? It cooks more quickly under increased pressure because it reaches a higher temperature.