Student Exploration: Carbon Cycle (ANSWER KEY)

Student Exploration: Phase Changes 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 pipes froze and pressure built up inside of them, causing them to burst.  

1. Spaghetti takes about 9 minutes to cook at sea level, but about 14 minutes in the mountains. Why do you think this is so?

 The difference in air pressure is most likely responsible for the considerable change in cooking time.   Gizmo Warm-upIn the Phase Changes Gizmo™, select the Micro view and set the Ice volume to 50 cc. Click Play () and observe molecules in the solid (ice), liquid (water), and gas (air) phases. 

1. In which phase(s) are the molecules held rigidly together?

 The solid phase.  

1. In which phase(s) do the molecules move freely?

 The gas phase     

1. In which phase(s) are the molecules held in a defined shape? The liquid phase

  

1. In which phase(s) do the molecules take the shape of their container? This happens in both

 the gas phase and the liquid phase.             

Activity A: Phase changes

Get the Gizmo ready: Click Reset () and select Macro view. Set the Water temperature to 10 °C. Set the Ice volume to 0 cc.

 Question: How is temperature related to phase changes? 

1. Predict: Based on your prior knowledge, predict the following:

 

1. At what temperature will water change from a liquid to a solid (freeze)? 0 degrees C

 

1. At what temperature will water change from a solid to a liquid (melt)? 1 degree C

 

1. At what temperature will water change from a liquid to a gas (boil)? 100 degrees C

  

1. 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:

 

1. At what temperature does water freeze?

1. At what temperature does ice melt.

 

1. At what temperature does water boil?

  

1. Observe: Set up the Gizmo to observe freezing. What do you notice about the temperature while the water is in the process of freezing

 

1. Explore: Use the Gizmo to investigate melting and boiling. Does the temperature change while either of these phase changes is occurring?.

 

1. 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?

   

1. Extend your thinking: Why do you think the temperature does not change much during a phase change?

  

Activity B: Temperature and molecular motion

Get the Gizmo ready: Click Reset, and select the Micro view. Set Ice volume to 0 cc. 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 

1. 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.

 

1. How does the mean speed of the water molecules change as they are heated?

  

1. Does the mean molecular speed change as much as the temperature as the water heats up? Explain.

  

1. Explain: How is temperature related to the motions of molecules?

1. Observe: Click Reset. Set the Water temperature to 20 °C and the Ice volume to 50 cc. 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?

   (Activity B continued on next page)Activity B (continued from previous page) 

1. Observe: Click Reset. Set the Water temperature to 100 °C and the Ice volume to 50 cc. Click Play. How does this situation compare to the previous one?

   

1. 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.

 

1. Ice is warmed to the melting point. _______________________________________

  

1. Water is warmed to the boiling point.

Temperature: Water is cooled to the freezing point.  

1. Extend your thinking: Click Reset. Set the Water temperature to 0 °C, the Ice volume to 0 cc, and Add/remove heat energy to -400 J/s. Click Play and wait until all the water freezes.

 

1. What volume of ice is created from 200 cc of water? _________________________

 

1. Why do water pipes sometimes burst in the winter

Activity C: Altitude and phase changes

Get the Gizmo ready: Click Reset. Set Ice volume to 0 cc. 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? (Circle your answers.)

 

1. Freezing point:                                                   Stay the same            Decrease

 

1. Melting point:                     Increase                   Stay the same           

 

1. Boiling point:                      Increase                   Stay the same           

1. 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:                              Melting point:                              Boiling point: 

1. Analyze: How did altitude affect the freezing, melting, and boiling points of water? 

1. 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.

1. Apply: Why does pasta take longer to cook in the mountains?

1. Apply: A pressure cooker allows food to be cooked under high pressure. Why is this useful?

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?