Science · 4th Grade · States of Matter and Their Changes · Weeks 28-36

Melting and Freezing

Observe and explain the processes of melting and freezing, focusing on the role of temperature.

• Common Core State Standards
• 2-PS1-4

About This Topic

Melting and freezing are reverse processes driven by adding or removing heat energy. When a solid melts, its particles gain enough energy to overcome the bonds holding them in place and begin moving freely as a liquid. When a liquid freezes, particles lose energy, slow down, and form the ordered structure of a solid. Both processes occur at the same temperature for a given substance -- the melting point -- which is a characteristic property of matter. Standard 2-PS1-4 guides students to observe and describe these changes using evidence.

In US 4th-grade classrooms, melting and freezing are typically introduced through investigations with water, wax, chocolate, or butter -- materials students encounter in daily life. Comparing different substances with different melting points helps students generalize the concept and see melting point as a useful identifying property.

Active learning strengthens this topic because it is built on prediction and evidence. When students predict the melting order of different substances, test their prediction, and revise their understanding, they practice science reasoning in a context that is concrete, safe, and engaging.

Key Questions

1. Explain what happens to the particles of a substance during melting.
2. Compare the energy changes involved in melting versus freezing.
3. Predict the melting point of an unknown solid based on its behavior.

Learning Objectives

• Compare the melting and freezing points of at least three different substances using observational data.
• Explain the particle behavior during the melting of a solid and the freezing of a liquid.
• Predict the order in which different substances will melt when exposed to the same heat source.
• Identify temperature as the key factor influencing melting and freezing processes.

Before You Start

Introduction to Matter

Why: Students need a basic understanding of solids and liquids to observe and describe changes between these states.

Properties of Solids and Liquids

Why: Familiarity with the characteristics of solids and liquids helps students identify and describe the changes they observe during melting and freezing.

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.
Melting Point	The specific temperature at which a solid substance begins to melt and turn into a liquid.
Temperature	A measure of how hot or cold something is, indicating the average kinetic energy of its particles.

Watch Out for These Misconceptions

Common Misconception

A larger piece of ice takes longer to melt because it has a higher melting point.

What to Teach Instead

Melting point is a property of the substance, not the amount. A larger piece takes longer because there is more material to melt, not because the melting temperature changes. Comparing small and large ice cubes in identical conditions helps students distinguish melting point from melting time.

Common Misconception

Melting and dissolving are the same process.

What to Teach Instead

Melting is a phase change caused by adding heat -- the substance becomes liquid. Dissolving involves one substance dispersing throughout another and is not caused by heat alone. Comparing ice melting in warm water versus salt dissolving in water makes the difference tangible.

Common Misconception

Freezing and cooling are the same thing.

What to Teach Instead

Cooling means reducing temperature; freezing is a specific phase change from liquid to solid that happens at a substance's freezing point. A liquid can be cooled without freezing if it does not reach that temperature. This distinction matters when predicting which materials will freeze under specific conditions.

Active Learning Ideas

Progettazione (Reggio Investigation): Melting Race

Give each group small samples of ice, butter, and chocolate at room temperature. Students predict which will melt first when placed in warm water, then observe and record actual melting order. Groups compare predictions with results and discuss what that tells them about each substance.

35 min·Small Groups

Think-Pair-Share: What Is a Melting Point?

After the investigation, ask: 'Why does ice always melt at the same temperature, no matter how big the piece is?' Partners discuss, then share ideas with the class. Guide students to the understanding that melting point is a property of the substance, not the amount.

15 min·Pairs

Observation Journal: Freezing Water Over Time

Students record observations of water placed in a freezer at regular intervals (or watch time-lapse footage). They sketch what they observe and label changes, then write an explanation of what is happening to the particles at each stage.

30 min·Individual

Gallery Walk: Melting and Freezing in Nature and Industry

Post stations with images and captions showing melting and freezing in real contexts: glaciers melting, steel being poured, candle wax solidifying, roads icing overnight. Students identify the process at each station and connect it to the energy change involved.

25 min·Small Groups

Real-World Connections

• Chefs use their knowledge of melting points to create specific textures in chocolate confections or to control the setting of butter in baked goods.
• Ice cream makers carefully control temperature to freeze liquid mixtures into the desired solid state, preventing large ice crystals from forming.
• Road crews in cold climates use salt to lower the freezing point of water, preventing ice from forming on roads and making travel safer.

Assessment Ideas

Exit Ticket

Provide students with a small cup containing ice cubes and another with a small amount of butter. Ask them to observe both over 5 minutes and write: 1. Which substance melted first and why? 2. What temperature change caused this to happen?

Quick Check

Present students with a chart showing three substances (e.g., water, chocolate, wax) and their known melting points. Ask: 'If you placed all three in a warm room, which would melt first? Which would melt last? Explain your reasoning.'

Discussion Prompt

Pose the question: 'Imagine you have a block of ice and a block of frozen juice. If you put them both outside on a warm, sunny day, what do you predict will happen? How does temperature play a role in your prediction?' Facilitate a class discussion on their ideas.

Frequently Asked Questions

What happens to particles when a solid melts?

When a solid melts, its particles gain heat energy and begin vibrating faster. Eventually, they gain enough energy to break free from their fixed positions and move past each other as a liquid. The substance looks different -- it flows and takes the shape of its container -- but the particles themselves are the same; they just have more energy and more freedom to move.

What is a melting point and why is it the same as the freezing point?

A substance's melting point is the temperature at which it changes from solid to liquid. The freezing point is the temperature at which it changes from liquid to solid. For any pure substance, these temperatures are identical -- water freezes and melts at 0 degrees C (32 degrees F), and iron freezes and melts at about 1,538 degrees C. The direction of the change depends on whether heat is being added or removed.

How is melting different from dissolving?

Melting is a phase change: a solid becomes a liquid when enough heat energy is added. Dissolving is when a substance (like sugar or salt) breaks apart and mixes evenly throughout another substance (like water). You can dissolve without heat (cold water dissolves sugar), and you can melt without dissolving (melting wax does not mix into anything -- it just becomes liquid wax).

How does active learning help students understand melting and freezing?

Prediction followed by hands-on observation is the most effective structure for this topic. When students predict which substance will melt first -- ice, butter, or chocolate -- and find out they were wrong, they are motivated to figure out why. This curiosity-driven revision of thinking builds a more durable understanding than reading about melting points in a text.