Changes of State: Melting and Freezing

Active learning works well for changes of state because students need to see, measure, and manipulate energy transfer to build a clear mental model of particles. The physical presence of ice, salt, wax, and thermometers makes abstract particle behavior concrete and memorable for young learners.

• Primary 4
• Science
• 4 activities
• 25 min–45 min

Learning Objectives

1. Explain the energy transfer that occurs during melting and freezing.
2. Compare the arrangement and movement of particles in a solid versus a liquid.
3. Predict the effect of impurities on the melting and freezing points of water.
4. Demonstrate the processes of melting and freezing using common materials.

Experiential Learning

⏱ 35 min·Small Groups

Fair Test: Salted Ice Melting

Provide identical ice cubes: one plain, one with salt, one wrapped in cloth. Students predict and time melting rates while measuring plate temperatures every 2 minutes. Groups discuss particle movement differences based on results.

Prepare & details

Explain the energy changes involved when a substance melts or freezes.

Facilitation Tip: During the Fair Test: Salted Ice Melting, remind students to start all ice cubes at the same size and temperature to ensure a fair comparison.

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

Experiential Learning

⏱ 25 min·Pairs

Particle Sorting Activity: Solid to Liquid

Give students beads in a tray to mimic solid arrangement, then shake gently to show liquid state. Add 'impurities' like larger beads and observe changes. Pairs sketch before-and-after models and explain energy roles.

Prepare & details

Compare the particle arrangement of a substance before and after melting.

Facilitation Tip: In the Particle Sorting Activity: Solid to Liquid, have students physically group labeled beads into solid, liquid, and gas piles before arranging them in order of movement.

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

Experiential Learning

⏱ 45 min·Whole Class

Freezing Race: Pure vs Impure Water

Students fill ice trays with plain water, saltwater, and sugar water at same volumes. Place in freezer, check hourly, and graph freezing times. Whole class compares data to predict real-world applications like de-icing.

Prepare & details

Predict how impurities might affect the melting or freezing point of a substance.

Facilitation Tip: For Freezing Race: Pure vs Impure Water, ask groups to predict which sample will freeze first and record their reasoning before starting the timer.

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

Experiential Learning

⏱ 30 min·Small Groups

Thermometer Tracking: Butter Melting

Heat butter portions slowly while monitoring temperatures. Students note when melting starts despite rising heat, linking to energy absorption. Record observations in tables for group sharing.

Prepare & details

Explain the energy changes involved when a substance melts or freezes.

Facilitation Tip: During Thermometer Tracking: Butter Melting, encourage students to note the exact moment the butter starts to soften and compare it to the temperature readings.

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

Teaching This Topic

Teach this topic by layering direct observation, measurement, and discussion. Start with hands-on experiments so students notice that melting and freezing happen at specific temperatures for each substance. Avoid rushing to explanations; let students articulate patterns first. Research shows that when students collect their own data and discuss it, their understanding of particle behavior deepens and sticks.

What to Expect

Successful learning looks like students using evidence from their experiments to explain how temperature changes cause particles to move differently in solids and liquids. They should confidently connect their observations to the particle model and apply this understanding to new situations.

Watch Out for These Misconceptions

Common Misconception

During the Fair Test: Salted Ice Melting, watch for students who believe melting requires direct flame or very high heat.

What to Teach Instead

Use this activity to show that ice melts at room temperature over time. Have students touch the ice cubes and observe particle movement without any flame, then discuss how gradual energy gain from the warm plate causes melting.

Common Misconception

During Freezing Race: Pure vs Impure Water, watch for students who think all liquids freeze at exactly 0°C.

What to Teach Instead

Guide students to compare the freezing times of salted and pure water. When the salted water freezes slower, ask them to explain how salt interferes with particle bonding, using their thermometer data as evidence.

Common Misconception

During the Particle Sorting Activity: Solid to Liquid, watch for students who think particles in liquids spread far apart and stop touching.

What to Teach Instead

Use the bead model to show that liquid particles touch but move freely. Have students shake the container gently and observe how beads stay close but change positions, reinforcing that spacing and movement differ from solids.

Assessment Ideas

Quick Check

After the Fair Test: Salted Ice Melting, ask students to record the temperature of the ice cubes at the start and end of the activity. Then, have them explain how the temperature change relates to the energy of the particles during melting.

Exit Ticket

During the Particle Sorting Activity: Solid to Liquid, collect each student's diagram of particle arrangements in solids and liquids along with a sentence explaining the key difference in particle movement between the two states.

Discussion Prompt

After the Freezing Race: Pure vs Impure Water, pose this question to small groups: 'If you add sugar to water before freezing it, do you think the mixture will freeze faster or slower? Explain your reasoning using what you learned about freezing points and particle behavior.'

Extensions & Scaffolding

• Challenge: Ask students to design their own experiment to test how different amounts of salt affect the melting time of ice cubes.
• Scaffolding: Provide a sentence starter for students to explain their predictions during the Freezing Race, such as 'I think the salted water will freeze first because...'.
• Deeper exploration: Have students research and present how changes of state are used in real-world applications like food preservation or making ice cream.

Key Vocabulary

Melting	The process where a solid changes into a liquid due to an increase in temperature and energy.
Freezing	The process where a liquid changes into a solid due to a decrease in temperature and energy.
Particle arrangement	How the tiny parts of a substance are organized, which differs in solids, liquids, and gases.
Melting point	The specific temperature at which a solid turns into a liquid.
Freezing point	The specific temperature at which a liquid turns into a solid.