Matter and Heat / Reversible Changes

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SWBAT claim the materials tested did not change properties when heat was added and support their claim with observations.

Big Idea

Students learn that adding or removing heat to material can be reversible.

NGSS Connections and Class Preparation

30 minutes

This lesson introduces the concept that when heat is added and removed from some materials, the change to the matter is reversible.

NGSS Standards

2-PS1-4 Construct an argument with evidence that some changes caused by heating or cooling can be reversed and some cannot. 

Students identify properties of crayons and lemonade and make observations as the material phases from solids to liquid and back again. Afterwards students claim whether the changes were reversible and support their claim with evidence.

Science Practices

- Analyzing and Interpreting Data (SP 4)

Students identify key properties and take observations of a material as it phases from a solid to a liquid and back again.

- Constructing Explanations (SP 6)

Students describe how the material changed from solid to liquid and back again when heat was removed and added and decide if it was a reversible change.

- Engaging in Argument from Evidence (SP 7)

Students review their observations to determine if after heat was added and removed from a material if the process was reversible. Then support their answer with their data. 

Cross-cutting Concepts - Appendix G

- Cause and Effect (XC 2)

 Students observe how adding or removing heat can cause a material to change phases.

Lesson Preparation

Collect 6 different colors of crayon pieces and peel off paper. Be sure to gather enough crayons to fill at least 6 molds.

I am choosing one color/mold so when I melt and cool the crayons, students will not be able to say the color property changed when I mixed the crayons.

Check that students have pages 2 and 3 of the 'Heat Transfer' booklet (See the previous lesson to copy the entire booklet). Or print Reversible Changes attached to this lesson.

Identify a heat source you can use, I am using a burner and pan with water, so the crayons do not get too hot.

Decide how students will see the melting of the crayons. I am using a document camera.

Write student names on small cups.



jars to place crayons in when melting double boiler style



extension cord

oven mitt

mold for melted crayons (I purchased a candy mold from Amazon)


small cups

popsicle sticks for lemonade taste observations

Other Ideas for melting crayon activities

Question for the Day

10 minutes

Science starts with a question, usually written on the board. This provides an opportunity for students to consider today's topic before the lesson has officially begun. 

I have established this routine with the kiddos to keep transition time short and effective and redirect student's attention back to content while allowing time for focused peer interaction.

Question for the Day: What are the properties of a crayon?

I want the kiddos  to articulate crayon properties so when I melt the crayons, students have criteria to reference as to whether or not the heat changed properties of the crayon.

Students turn to their partner and share their ideas. When students turn to face me, to indicate they have finished sharing, I call volunteers to share what their partner said.

Sharing what their partner said encourages active listening.

I write student responses on the board.

"As we learned in the last lesson, matter can change its phase when heat is added or removed. If I add heat to the crayons they will ...? Right, melt or turn into a liquid."

When the substance cools what will it turn into? Right a solid, will it still be a crayon? Please discuss this with a different shoulder partner."

I listen to conversations to hear how students support their claim and to get an idea for experiences they may had with melting crayons.

"I heard some interesting hypothesizes, what would a scientist do? Yes test it!"

I use the document camera as I show students the next step.

"I will place some crayons in this pot and add heat with the burner to melt the crayons. Then we will observe what happens with the crayon matter when it cools, or heat is removed."

"Before I melt the crayons, please return to your desk and take out your lab booklet that we used in the last lesson. Turn to page 3.

Crayon Observations

30 minutes

Page 2 in their lab booklet:

"Let's review the crayon properties that your classmates shared. Which properties best describe a crayon and why?" I star these.

"On page 3, at the top of the page, list the crayon properties that you think best describe a crayon, you may write the words we stared. Your crayon property list will help you decide if the final material is a crayon or not."

"Let's fill out the table together. The crayon matter phase is...? Right, a solid. How do we know that it is a solid?"

"I am going to place the crayon(s) in the pan and turn on the burner. Am I adding or removing heat? Right, go ahead and fill in the next part of the table."

I have already turned on the burner so students can see the crayon melting. After the crayon has completely melted, I move the jar with the melted crayon so student see that it is a liquid. Students write, 'liquid' in the next box and in the first box on the 2nd row.

I had a couple of students who mislabeled the crayon phase on the 2nd row, they wrote solid. I will direct students to check their table partner's work next time. 

While it is still in its liquid form, I pour it into molds which are under the document camera. I direct students to discuss what will happen as the crayon cools is heat being added or removed. Then students fill in the next part of the table.

When the crayons have solidified. I pop them out of the molds. I pass out the molded crayons and direct students to write their observations about the material they are looking at now. This information goes in the last box on the 2nd row.

I do not use the word crayon, as I want the students to decide for themselves if the new material is a still a crayon or not.

Finally students discuss and answer the question if the final solid material they made observations  about, is a crayon.

I walk around the room to listen to discussions and read what they wrote. I remind students to back up their answer with their property list and final observations. 

When most students have completed their discussions and/or writing their explanations, I ask students to show me with their hand who thought the new material was still a crayon and who thought we made a new material.

If some students explain that it is a new material because it is not shaped the same, I use two different size papers and ask if these are both pieces of paper.

"So, with the crayon I was able to add heat and change the phase of the crayon from solid to liquid and the remove heat and change the liquid crayon to solid. The crayon went back and forth from solid to liquid and back to solid. We call this a reversible change."

"Do you think crayons are the only material that we heat and cool or freeze and warm and it keeps it properties? Show me with your thumbs."

"Let's test one more material, but this time we will remove heat and then warm it to see if it is reversible material."


Setting up for Lemonade Pops

15 minutes

Page 3

I am sure that most students will argue correctly that lemonade when frozen and thawed will be lemonade, but I want to demonstrate how scientists would prove an argument with scientific testing.

"We will start this test today, but will not be able to finish it till the material is frozen. When we freeze a material is heat removed or added?"

I pass out small paper cups of lemonade, with the student's name printed on the side. On page 4 students write the properties of the liquid.

"You always want to be very careful about taste testing any material. This material is o.k. to test, it is lemonade." I show them the lemonade container. "So you can use your sense of taste to describe the properties of the lemonade."

I pass out popsicle sticks to use for taste observations.

After students have completed their property list for the lemonade. I collect the paper cups and will place them in the freezer.

Students place their lab booklet in their science folder and meet me on the rug.


5 minutes

"What is another example of matter that can change back and forth from solid to liquid and back again and still keep its essential properties, those properties that help us know that specific material or matter?"

If students are not sure, I will remind them of the water cycle. "Right water!"

"What did we learn about material and adding and removing heat? Yes, that some materials are reversible. Heat can be added or removed and it does not change the material."

"When we meet for science next time you will finish your lab on the lemonade and then we will test some other materials."