Changes of State: Melting and Freezing

Active learning helps students visualize particle motion during melting and freezing, which is invisible at the macroscopic level. Hands-on stations and investigations build evidence about how energy changes affect states of matter, making abstract concepts concrete and memorable for young scientists.

• 5th Year
• Foundations of Matter and Chemical Change
• 4 activities
• 20 min–45 min

Learning Objectives

1. Compare the physical properties of water in its solid (ice) and liquid states.
2. Explain the particle behavior during the melting and freezing of water.
3. Identify the melting point and freezing point of water under standard atmospheric pressure.
4. Demonstrate the reversibility of the melting and freezing processes for water.

Stations Rotation

⏱ 35 min·Small Groups

Stations Rotation: Melting Challenges

Set up stations with ice cubes: one at room temperature, one in warm water, one with salt sprinkled on top, and one wrapped in cloth. Small groups rotate every 7 minutes, timing melts and noting temperatures. Groups share data to compare effects.

Prepare & details

What happens to ice when it gets warm?

Facilitation Tip: During Station Rotation: Melting Challenges, circulate with a timer to ensure students rotate every 8 minutes so they experience multiple materials and temperature probes.

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

⏱ 45 min·Pairs

Freezing Point Investigation

Pairs fill trays with water samples: pure water, saltwater, and sugared water. Place in freezer and check hourly, recording first ice formation times. Discuss why impurities affect freezing points using particle explanations.

Prepare & details

How can we turn water back into ice?

Facilitation Tip: For Freezing Point Investigation, remind students to record temperatures every 30 seconds to capture the plateau at 0°C clearly on their graphs.

⏱ 25 min·Individual

Melting Curve Graphing

Individuals track temperature of melting ice every 30 seconds for 10 minutes, plotting points on graphs. Compare class graphs to identify the plateau at 0°C. Extend by repeating with added salt.

Prepare & details

Does everything melt and freeze at the same temperature?

Facilitation Tip: In Melting Curve Graphing, provide graph paper with pre-labeled axes to save time and reduce frustration, allowing focus on data interpretation.

⏱ 20 min·Whole Class

Reversible Change Demo

Whole class observes a large ice block melting in a heated bowl, then refreezing poured water overnight. Vote on predictions beforehand and revisit results next lesson to confirm reversibility.

Prepare & details

What happens to ice when it gets warm?

Facilitation Tip: During Reversible Change Demo, ask each pair to prepare a 30-second explanation of their observations before sharing with the class to build confidence.

Teaching This Topic

Start with a quick demonstration of ice melting in a beaker while students sketch particle arrangements at each stage. Use guided questions to connect energy input to particle behavior, avoiding jargon like 'latent heat' until later. Research shows that students need multiple opportunities to observe and explain before formalizing vocabulary, so keep explanations simple and repeatable across activities.

What to Expect

Students should explain melting and freezing using particle movement terms like energy gain or loss, vibration, and arrangement. They should also recognize that these changes are reversible and do not alter the substance itself, demonstrated through observations and measurements at each station.

Watch Out for These Misconceptions

Common Misconception

During Station Rotation: Melting Challenges, watch for students assuming all substances melt at 0°C.

What to Teach Instead

Use thermometers to measure the melting points of ice, chocolate, and wax at each station. Have students compare their data in small groups and identify that different substances have unique melting points, reinforcing that water's 0°C is not universal.

Common Misconception

During Reversible Change Demo, watch for students describing melting as a chemical change that changes the substance.

What to Teach Instead

Ask students to taste the water before and after freezing to confirm it remains water. Use their observations to discuss how particle arrangement changes but the substance stays the same, linking back to the demo materials.

Common Misconception

During Freezing Point Investigation, watch for students expecting water to contract when freezing like most liquids.

What to Teach Instead

Have students measure the volume of water before and after freezing using a balloon or graduated cylinder. Discuss how the expansion is due to the open crystal lattice of ice, visible in the balloon experiment, and relate it to real-world examples like bursting pipes in winter.

Assessment Ideas

Exit Ticket

After Station Rotation: Melting Challenges, provide students with two beakers—one with ice cubes and one with liquid water at room temperature. Ask them to write one sentence describing what will happen to the ice cubes if left out and one sentence describing what will happen to the liquid water if placed in a freezer, referencing particle movement.

Quick Check

During Melting Curve Graphing, display a graph showing the temperature of water over time as it melts and then freezes. Ask students to identify the melting point and freezing point on the graph and explain what is happening to the particles at each point using the graph data.

Discussion Prompt

During Freezing Point Investigation, pose the question: 'If you add salt to water, does it freeze at the same temperature? Why or why not?' Facilitate a class discussion where students share initial ideas and then use their data from the activity to explain how impurities affect freezing points.

Extensions & Scaffolding

• Challenge students to predict and test how adding salt affects the melting time of ice cubes at each station, then graph the results.
• Scaffolding for struggling students: Provide a word bank with terms like 'vibrate,' 'slide,' 'lock,' and 'energy' to help them describe observations during the Reversible Change Demo.
• Deeper exploration: Have students research how the expansion of water when freezing affects ecosystems, such as how ice forms on lakes and supports aquatic life.

Key Vocabulary

Melting	The process where a solid changes into a liquid due to an increase in temperature and kinetic energy of its particles.
Freezing	The process where a liquid changes into a solid due to a decrease in temperature and kinetic energy of its particles.
Melting Point	The specific temperature at which a solid substance begins to melt and change into a liquid. For water, this is 0°C.
Freezing Point	The specific temperature at which a liquid substance begins to freeze and change into a solid. For water, this is 0°C.
Particle Kinetic Energy	The energy of motion possessed by the individual particles (atoms or molecules) within a substance, which increases with temperature.