Lesson ​4
States of Matter: Changes with Temperature
Learners observe how many materials, especially water, shift between solid, liquid, and gas states as temperature changes. They finish the lesson by discovering that all states of matter share two key attributes: they take up space and they have weight.

Key Ideas
  • Temperature determines what state a material is in. Most materials can exist as a solid, liquid, or gas depending on how hot or cold they are. We see this most clearly with water.
  • Raising temperature causes melting (solid to liquid). Lowering temperature causes freezing (liquid to solid). Heating further causes evaporation (liquid to gas).
  • All solids, liquids, and gases together are called MATTER. Matter has weight and takes up space. Heat and light do not take up space and have no weight. They belong to a different category entirely: energy.

Supplies:

  • Not required, but I recommend demonstrating changes in states of matter with an ice cube and with boiling water.
  • Chart (Solid Liquid Gas Chart) is optional

Vocabulary
  • Melting: The change from solid to liquid caused by raising temperature.
  • Freezing: The change from liquid to solid caused by lowering temperature.
  • Evaporation: The change from liquid to gas caused by raising temperature.
  • Condensation: The change from gas to liquid caused by lowering temperature.
  • Energy: Something that makes things move, change, or happen. Heat and light are forms of energy, not matter.

Discussion Questions
  • If heat causes things to melt, why does the sun not melt rocks on Earth?
  • Water is unusual because it expands when it freezes instead of shrinking like most substances. Why do you think this matters for life on Earth?
  • Is there a temperature at which everything in the universe would be a gas? Is there a temperature at which everything would be a solid?

Hands-On Activity: Chocolate in Your Hand

Lab Sheet 

Supply List
  • Small pieces of chocolate (one piece per student, plus one extra wrapped in foil)
  • Aluminum foil
  • A plate or tray
  • A freezer or refrigerator with space to place the melted chocolate
  • Notebook and pencil

Instructions
  • Hold one piece of chocolate directly in your palm. Wrap the other identical piece tightly in foil and hold it in your other hand.
  • Wait about two to three minutes without squeezing either piece. Observe what happens to each.
  • Unwrap both and compare. The direct piece melted; the foil piece likely stayed mostly solid. Discuss: what was the only difference between the two? What caused the change?
  • Pour the melted chocolate onto a small piece of foil and place it in the freezer or refrigerator. Wait until it solidifies again.
  • Examine the re-hardened chocolate. Is it still chocolate? What changed and what stayed the same?
  • Discuss: was this change caused by temperature? Can it be reversed by changing temperature back? What other materials behave this way?

Digging Deeper Topic
Sources

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L4 Changes in Temperature by Selene

Phet State of Matter Basics Simulation

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