Science · 1st Grade · Properties of Materials · Weeks 19-27

Changing Materials: Heating and Cooling

Students investigate how heating and cooling can change the properties of some materials.

• Common Core State Standards
• 2-PS1-4

About This Topic

Students in first grade can observe that some materials look or behave differently after being heated or cooled, and that these changes are not always reversible. Standard 2-PS1-4 asks students to construct an argument with evidence that some changes caused by heating or cooling can be reversed and some cannot. Ice melts when heated but can be frozen again when cooled, making the change reversible. A cookie baked in the oven cannot be unbaked; that change is permanent.

The examples students encounter in this topic are highly familiar. Butter melts on warm toast. Chocolate softens in a warm hand. Ice cream melts in a cup. Connecting these everyday experiences to the scientific concept of reversible and irreversible changes gives students the vocabulary to describe something they already know but may not have analyzed carefully.

Active learning is ideal for this topic because the changes happen in real time during investigation. Watching ice melt and then predicting what would happen if you put the water back in the freezer, then verifying that prediction the next day, creates a direct evidence cycle. The ability to observe, predict, test, and reflect within a single lesson sequence makes this one of the most naturally engaging topics in first-grade science.

Key Questions

1. Explain how heating can change the state or properties of a material.
2. Compare the effects of heating and cooling on different substances.
3. Predict what might happen to a material if it is heated or cooled significantly.

Learning Objectives

• Classify materials as having reversible or irreversible changes when heated or cooled.
• Explain how adding or removing heat energy causes observable changes in materials.
• Compare the effects of heating and cooling on at least three different substances.
• Predict the outcome of heating or cooling a given material based on prior investigations.

Before You Start

Observing Properties of Objects

Why: Students need to be able to observe and describe the characteristics of objects before they can identify changes to those characteristics.

Basic Needs of Plants and Animals

Why: This unit often involves exploring how temperature affects living things, such as plants wilting in heat or animals seeking shade.

Key Vocabulary

Heat	Energy that makes things warm. Adding heat can make materials change.
Cool	To make something less warm. Removing heat can make materials change.
Reversible change	A change that can be undone, like melting ice and then freezing it again.
Irreversible change	A change that cannot be undone, like baking a cake or burning paper.
Melt	To change from a solid to a liquid because of heat.
Freeze	To change from a liquid to a solid because of cooling.

Watch Out for These Misconceptions

Common Misconception

Heating always melts materials.

What to Teach Instead

Students overgeneralize from familiar examples like ice or butter. Materials like wood, bread, and eggs undergo very different changes when heated, including burning or hardening. Testing varied materials rather than just focusing on melting helps students see that heating can cause many different types of changes depending on the material.

Common Misconception

All changes caused by heating or cooling can be reversed.

What to Teach Instead

Students who have observed ice melting and refreezing may assume all heat-related changes are reversible. Comparing the ice cycle to a cooked egg or toasted bread, where the change is permanent, establishes the distinction. Asking 'can you untoast bread?' grounds the concept in concrete, accessible experience.

Common Misconception

The material disappears when it melts.

What to Teach Instead

Young students sometimes think a melted ice cube is 'gone.' Weighing the ice before melting and the water after shows that the same amount of material is present; it just changed state. This is an important early introduction to conservation of matter, even if that vocabulary is not used at the first-grade level.

Active Learning Ideas

Inquiry Circle: Ice Cube Investigation

Small groups receive ice cubes and predict what will happen if the ice is left in a cup on the desk, recording which properties they think will change. They observe over 20 minutes, noting temperature, state, and appearance changes. After the ice melts, they predict what would happen if they could freeze the water again and discuss whether they think this is a reversible change.

30 min·Small Groups

Gallery Walk: Reversible or Not?

Post photos of eight change events around the room: ice melting, butter melting, wood burning, an egg cooking, chocolate melting, paper tearing, clay being shaped, and bread toasting. Students walk around and for each photo indicate whether they think the change is reversible or not, writing one reason for their choice.

25 min·Individual

Think-Pair-Share: What Changed and Can We Undo It?

Show students a melted crayon that hardened into a new shape. Ask what happened when it was heated, what happened when it cooled, and whether the original crayon still exists in some form. Students pair to construct an explanation, then share with the class. The teacher connects this to reversible changes where material composition has not changed.

20 min·Pairs

Simulation Game: Prediction Chain

The teacher presents a series of heating and cooling scenarios using a photo sequence. Students predict the next state in the sequence, such as what a hot ice cube becomes, what frozen juice becomes when left out, and what melted chocolate becomes when cooled. After predicting each step, students classify the overall change as reversible or requiring more investigation.

20 min·Whole Class

Real-World Connections

• Bakers use ovens to heat dough, causing irreversible changes that transform it into bread or cookies. They cannot unbake these items once they are cooked.
• Chefs and food scientists understand how cooling affects food, such as freezing ice cream or chilling liquids to change their texture and state for consumption.
• Candymakers carefully control heating and cooling processes to create different types of candy, like hard candy from melted sugar or soft caramels.

Assessment Ideas

Quick Check

Show students pictures of common items like an ice cube, a chocolate chip, and a piece of toast. Ask them to point to or say whether heating would make it melt or change permanently, and whether cooling would make it freeze or change permanently. Record their responses.

Exit Ticket

Provide students with two index cards. On one card, they draw a picture of something that changes reversibly when heated or cooled. On the other card, they draw something that changes irreversibly. They should label each drawing.

Discussion Prompt

Ask students: 'Imagine you have a stick of butter and a raw egg. If you heat both, what happens? Which change can you undo, and which can you not undo? Why is it important for cooks to know the difference?'

Frequently Asked Questions

What is the difference between a reversible and an irreversible change?

A reversible change is one where the material can go back to its original form. Ice melting to water is reversible because you can freeze the water again and get ice back. An irreversible change is permanent. Once bread is toasted or an egg is cooked, you cannot return them to their original form. The material has changed in a way that cannot be undone.

Why does ice turn into water when it gets warm?

Ice is water in solid form. When heat energy is added, the water molecules start moving faster and the rigid structure of the ice breaks apart. The result is liquid water. The material is the same throughout; only its state changes. Cool the liquid water back down and the molecules slow down again and re-form the solid ice structure.

How can active learning help students understand heating and cooling changes?

Observing real changes in real time makes the abstract concept of state change concrete and visible. When students watch an ice cube melt and then predict whether the water would freeze back into ice, they are constructing and testing a scientific claim. Comparing that reversible change to an irreversible one like a baked cookie sharpens the distinction in a way that descriptions alone cannot achieve.

What are some safe examples of heating and cooling changes to explore in a 1st grade classroom?

Safe options include observing ice cubes melt at room temperature, examining butter softening in warm water, shaping and reshaping clay to show reversible change, and comparing fresh dough to baked bread to show irreversible change. Chocolate chips melted in a warm hand and then cooled on a cold surface demonstrate both melting and re-solidifying safely without any heat source.