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Phase Changes


  Welcome to the student exploration of phase changes! This webquest will help illustrate how molecular motion is related to phase changes.
Some Background Info
Solids are characterized by atoms or molecules held in a rigid structure. Liquids are characterized by molecules that are attracted to one another but can still move around so that they take the shape of their container. Gases are characterized by rapidly moving molecules that move and collide freely.
When a solid is heated, atoms vibrate more rapidly. During the melting process, temperature does not increase because the added heat energy goes into melting the solid rather than heating the liquid.
In a liquid, the molecules move at a variety of speeds. Evaporation and boiling happens when a liquid is heated. The temperature remains constant during boiling because the fastest molecules are constantly leaving the liquid and escaping as gas. When a liquid is cooled, the molecules move slowly enough that they can begin to form rigid chemical bonds in a crystalline lattice. This is freezing.
  Explore the various websites provided to complete the Phase change worksheet. This will help use understand phase changes.
  1. Please answer the prior knowledge questions before moving on...
2. Go to and explore solids, liquids, gases, boiling, melting, and freezing points.
3. Go to the first website and observe molecules in the solid, liquid, and gas phases. Answer questions on first page of worksheet.
4. Make your predictions on top of page 2 of worksheet. Go to and read about freezing point, melting point, and boiling point of water.
5. Boiling Experiment: Boil water on a hot plate. Every two minutes record the temperature of the water until it boils. Fill out a lab write up according to the board. Watch this video discussing phase changes in a heating curve. (Chemistry music video 6: heating curve). Use this information to answer the next set of questions.
5. Go to
Answer questions on the third page based on the new information you learned from this site.
6. Watch this youtube video to answer question 6.
7. Go to Read under the sections Melting and boiling points vary with pressure and Lowered boiling point of H2O to help you answer the last page.
  Websites to go to:
If you are having trouble clicking to the link, copy and paste it into a new Firefox window.
  Turn in completed worksheet! Put Lab write up into your notebook and in your table of contents.
Please go to log in with the user name guest, password guest. Click play, then level 2 heating curve. Play the game to show your understanding of the heating curve with boiling, melting, and freezing points. Put your points on the top right corner of you lab write up.
  1. What are some of the differences between solids, liquids, and gases?
2. How does temperature relate to molecular motion?
3. What causes materials to change phase?
4. Why does the temperature stay constant during a phase change?
5. Why do water pipes burst in the winter?
6. Why does it take longer to cook pasta at high altitudes than at sea level?

This Web Quest is available at