Changes of state are physical changes that occur when matter absorbs or loses energy. Processes in which matter changes state include freezing, melting, vaporization, evaporation, condensation, sublimation, and deposition.
- SCI.CA.8.PS.3.d; SCI.CA.8.PS.7.c
- AAAS.6-8.4.D.5, 6, 14, 16
- Explain the role of energy in changes of state.
- Outline the processes of freezing and melting.
- Describe vaporization and condensation.
- Define sublimation and deposition.
condensation: process in which a gas changes to a liquid
deposition: process in which a gas changes directly to a solid without going through the liquid state
evaporation: process in which a liquid changes to a gas without boiling
freezing: process in which a liquid changes to a solid
melting: process in which a solid changes to a liquid
sublimation: process in which a solid changes directly to a gas without going through the liquid state
temperature: average kinetic energy of particles of matter
vaporization: process in which a liquid boils and changes to a gas
Introducing the Lesson
Review states of matter and introduce changes of state with the resources at the following URL. As students enter the classroom, play the karaoke song while displaying the lyrics on a screen, and encourage students to sing along. Then show the 3-minute video. After the video, ask students what they learned about changes of state from the video. Tell them they will learn more about changes of state in this lesson. If you want to extend this introduction, click on the “Teacher Guide” at the Web site for more ideas.
Call students’ attention to the picture of the pothole puddle in the FlexBook® lesson.
Question: If the same amount of rainwater fell into a broader, shallower pothole, which puddle would evaporate more quickly?
Answer: The water in the broader, shallower pothole would evaporate more quickly because it would have more surface area exposed to the air. This would allow more water molecules to escape into the air at the same time (assuming other conditions such as temperature are the same).
Have students play the game at the following URL to apply their knowledge of the processes involved in changes of state.
Students are likely to have first-hand experience with all of the changes of state described in the lesson with the possible exception of sublimation. Demonstrate sublimation by placing dry ice (solid carbon dioxide) in a clear glass container. Have students observe as the solid dry ice changes directly into carbon dioxide gas without passing through the liquid state.
Make changes of state more concrete by using a familiar example—water. Draw a cycle diagram like the one below, and have students label the arrows with the correct processes.
Ask a few students who need extra challenges to learn how matter changes to the plasma state. They can start with the URLs below. Have them share what they learn in an oral report.
With the activity at the following URL, students can design and conduct their own experiment to find out how heating water affects the rate of evaporation. In the activity, they will identify variables and controls and draw conclusions from their observations. The Web site provides complete teacher instructions, a student activity sheet, background reading, and extensions to the activity.
Researchers have identified several common misconceptions that students may hold about how matter changes state. Two are listed below. Read the misconceptions to the class and call on volunteers to restate them as true statements. Additional misconceptions are available at this URL: http://beyondpenguins.ehe.osu.edu/issue/water-ice-and-snow/common-misconceptions-about-states-and-changes-of-matter-and-the-water-cycle.
Misconception: Water in an open container disappears because it changes into air.
True statement: Water in an open container evaporates, or changes from liquid water to water vapor.
Misconception: Drops of water on the outside of a cold glass have seeped, or “sweated,” through the glass.
True statement: The drops of water have condensed from water vapor in the air that came into contact with the cold glass.
Reinforce and Review
Copy and distribute the lesson worksheets in the CK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Check students’ mastery of the lesson with Lesson 4.3 Quiz in CK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
In this chapter, you read that atoms and molecules of the same kind of matter have forces of attraction between them. Atoms consist of even smaller particles. These particles are held together by certain forces as well.
- What are the particles that make up atoms?
- What forces might hold them together?