Changing States: Melting and Freezing

Active learning helps students grasp the difference between reversible and irreversible changes by making abstract ideas concrete. Through hands-on experiments with melting, freezing, and reactions, students see firsthand how some changes can be reversed while others cannot.

• Year 5
• Science
• 3 activities
• 20 min–60 min

Learning Objectives

1. Explain the particle behavior during melting and freezing.
2. Analyze the relationship between temperature and the rate of ice melting.
3. Compare the melting and freezing points of different substances.
4. Predict the state of a substance at a given temperature based on its melting and freezing points.

Experiential Learning

⏱ 45 min·Small Groups

Predict-Observe-Explain: The Mystery Reactions

Provide students with several scenarios, such as mixing vinegar and milk or melting chocolate. Students predict if the change is reversible, observe the reaction in small groups, and then write an explanation using evidence like 'no new material was formed' or 'a gas was produced'.

Prepare & details

Explain what happens to the particles of a substance when it melts or freezes.

Facilitation Tip: During Predict-Observe-Explain, pause after predictions to let students discuss their ideas in pairs before revealing the reactions to deepen engagement.

Setup: Varies; may include outdoor space, lab, or community setting

Materials: Experience setup materials, Reflection journal with prompts, Observation worksheet, Connection-to-content framework

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Stations Rotation

⏱ 60 min·Small Groups

Stations Rotation: Recovery Lab

Students visit stations where a change has already occurred, such as salt dissolved in water or a burnt piece of paper. Their task is to brainstorm and, where possible, attempt a method to reverse the change, such as using evaporation or filtration, to see which materials can be recovered.

Prepare & details

Analyze how temperature affects the rate at which ice melts.

Facilitation Tip: In the Recovery Lab, set up stations so students rotate in small groups to encourage peer teaching and shared observation of reversible changes.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Think-Pair-Share

⏱ 20 min·Pairs

Think-Pair-Share: The Kitchen Scientist

Students think of three changes that happen during cooking, such as frying an egg, boiling water, or making toast. They pair up to categorize these as reversible or irreversible and then share their reasoning with the class, focusing on whether a new substance was created.

Prepare & details

Predict whether a substance will melt or freeze at a given temperature.

Facilitation Tip: In Think-Pair-Share, assign specific roles (recorder, reporter) to ensure all students contribute and stay accountable during discussions.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Teaching This Topic

Experienced teachers approach this topic by building on students’ everyday experiences, such as ice melting into water or chocolate softening in a pocket. Use real substances like wax or ice to make the concepts tangible, avoiding abstract diagrams until students have solidified their understanding. Research shows that concrete examples reduce misconceptions about states of matter and reinforce the idea that changes in state are physical, not chemical. Avoid overemphasizing heat as the sole cause of change, since cooling is equally important to reversing the process.

What to Expect

Students will confidently identify reversible changes like melting and freezing, explain why dissolving or mixing can be undone, and distinguish these from irreversible changes by describing the materials before and after each process. They will use accurate vocabulary and support their reasoning with evidence from their investigations.

Watch Out for These Misconceptions

Common Misconception

During Predict-Observe-Explain: The Mystery Reactions, watch for students assuming that any reaction requiring heat is irreversible.

What to Teach Instead

Use the wax or chocolate melting activity to demonstrate that heating can reverse the change when cooled again, contrasting this with the vinegar and bicarbonate reaction which produces a new gas.

Common Misconception

During Station Rotation: Recovery Lab, watch for students thinking that gases produced in reactions have disappeared.

What to Teach Instead

Have students capture the gas from the vinegar and bicarbonate reaction in a balloon and observe that the balloon inflates, showing the gas still exists and can be measured by size.

Assessment Ideas

Exit Ticket

After Predict-Observe-Explain, ask students to write whether the melting and freezing of wax was reversible or irreversible and explain why, using evidence from their observations.

Quick Check

During Station Rotation: Recovery Lab, circulate and ask students to point to the station where a new substance was formed and explain how they know it’s irreversible.

Discussion Prompt

After Think-Pair-Share: The Kitchen Scientist, have pairs share their examples of reversible changes in cooking, then hold a class vote on whether each example is reversible or irreversible, using the terms melting, freezing, and dissolving.

Extensions & Scaffolding

• Challenge: Ask students to design a simple experiment to test whether dissolving salt in water is reversible. They should plan how to recover the salt and present their method to the class.
• Scaffolding: Provide a word bank with terms like solid, liquid, gas, melt, freeze, and dissolve to support students in writing or speaking about their observations.
• Deeper exploration: Introduce the concept of sublimation by showing dry ice (solid carbon dioxide) changing directly into gas, and have students compare it to melting and freezing changes.

Key Vocabulary

Melting	The process where a solid changes into a liquid due to an increase in temperature.
Freezing	The process where a liquid changes into a solid due to a decrease in temperature.
Reversible Change	A change where the original substance can be recovered, such as melting and freezing.
Melting Point	The specific temperature at which a solid substance turns into a liquid.
Freezing Point	The specific temperature at which a liquid substance turns into a solid.