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PhaseChangesSEKey

Explore the behavior of water molecules in solid, liquid, and gas phases. Observe how molecular motion and arrangement change with state. Great for visualizing states of matter!

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    Phase Changes Answer Key Vocabulary: altitude, boil, boiling point, freeze, freezing point, gas, liquid, melt, melting point, phase, solid Prior Knowledge Questions (Do these BEFORE using the Gizmo.) /Atote: The purpose of these questions is to activate prior knowledge and get students thinking. Students are not expected to know the answers to the Prior Knowledge Questions.] Marla wants a hard-boiled egg for breakfast. The recipe says boil water, then lower the heat so the water is simmering. But Marla is in a rush, so she keeps the heat on high as the egg cooks. Do you think the egg will be done faster if the heat is kept on high as the water boils? Answers vw// vary [Correct answer is no.] Explain your answer. Bcp/anations vw// vary. [The boiling temperature of water is constant, s o the egg will take the same amount of time to cook no matter what the burner is set to.] Gizmo Warm-up In the Phase Changes Gizmo, select Micro view. Notice the nitrogen (*?»), oxygen ($), and water ( P ) molecules. To start, create ice. Set Ad d/r emove heat energy to -200 J/s, click Play ( * ), and then click Pause ( ) when the container is about half ice, half water. Set Add/remove heat energy back to 0 J/s, and then click Play. 1. Observe water molecules in the solid (ice), liquid (water), and gas (air) phases. A. In which phase(s) do molecules move freely? Gas anOquid B. In which phase(s) are molecules held together? Solid C. What do you notice about the positions of the ice molecules? They form hexagons. When frozen, water molecules form a hexagon (six-sided shape) pattern. 2. Click Reset { ■ s ) : and select Macro view. Set the Ice volume to 25 c m 3 . A. In which phase(s) is water held in a defined shape? Sofid B. In which phase(s) does the water take the shape of the container? L/qutd and gas

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    Activity A: Phase changes Get the Gizmo ready: • Click Reset ( o ) and select Macro view. • Set the Water temperature to 10 “C. • Set the Ice volume to 0 cm 3 . ;J ■ I Question: How i s temperature related to phase changes? 1. Predict: Based on your prior knowledge, predict the following: Precficfrcvis vwfl vary. A. At what temperature will water change from a liquid to a solid (freeze)? B. At what temperature will water change from a solid to a liquid (melt)? C. At what temperature will water change from a liquid to a gas (boil)? 2. Investigate: Use the Gizmo to explore phase changes. Use the Addfremove 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 °C B. At what temperature does ice melt? 0 °C C. At what temperature does water boil? JOO °C This is the freezing point This is the melting point. 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? The temperature remains constant. 4. Explore: Use the Gizmo to investigate melting and boiling. Does the temperature change while either of these phase changes is occurring? Vo, the temperature is constant. 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? During the phase changes, the graph shows a flat tine. 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. Answers wifl vary. [During melting or boiling, heat energy is used to break the intermofecular forces (intermofecufar bond) between molecules rather than speed them up. During freezing, heat energy is released by the formation of intermofecufar bonds between molecules.]

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