Skip to main content
NGSS*2nd GradePhysical Science

2-PS1-4: Changes from Heating and Cooling

Also called NGSS 2-PS1-4 · Topic: Structure and Properties of Matter · Physical Science

All 14 2nd Grade Science Standards

The Official Wording

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

Clarification statement: Examples of reversible changes could include materials such as water and butter at different temperatures. Examples of irreversible changes could include cooking an egg, freezing a plant leaf, and heating paper.

NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026

What 2-PS1-4 Means in Plain English

Second graders heat and cool everyday materials and watch what happens. Then they make a claim, backed by what they saw, that some of these changes can be undone, like chocolate melting and hardening again, while others, like bread turning into toast, cannot.

Students describe the changes they observe and do not need to explain them with particles or chemistry. Later, 5th graders show that mixing some substances makes a new substance (5-PS1-4) and that total weight stays the same through a change (5-PS1-2).

2-PS1-4 I Can Statements

  • I can describe how heating or cooling changed a material.
  • I can tell a change that can be undone from one that cannot.
  • I can use what I saw as evidence for my claim.

2-PS1-4 Worked Example

A heat-and-cool test with a bag of chocolate chips and two slices of bread.

The Question

After heating, can chocolate chips and bread go back to the way they were?

Set It Up: A handful of chocolate chips in a sealed zip bag, a bowl of warm tap water, a bowl of ice water, and two slices of bread with an adult-run toaster.

Chocolate and bread, hot and cold
Warm waterChips in bagIce waterBreadToaster heat
What Students Do
  1. Float the bag of chips in the warm water bath for five minutes.Chips melt into a soft puddle
  2. Move the bag into the ice water for ten minutes.Chocolate is hard, in a new flat shape
  3. Have an adult toast one slice and keep the other plain.Toast is brown, crisp and smells different
  4. Let the toast cool for ten minutes, then compare it with the plain slice.Brown and crisp, unchanged by cooling
  5. Sort each change on a chart: can be undone or cannot.Chocolate: can undo. Toast: cannot
What They Find

The melted chocolate became solid when it cooled, but the toast stayed toast after cooling.

Why it works: Melting and hardening change a material's form but not what it is, while toasting makes bread into something new that cooling cannot undo.

Common Mistakes with 2-PS1-4

Calling every change permanent

“The chocolate is ruined because it melted”

Try this: Cool the melted material and look again. If it goes back to being a solid, the change can be undone.

Expecting the exact old shape

“It’s not chips anymore, so it didn’t go back”

Try this: Focus on the material, not the shape. The chocolate is solid chocolate again even though it hardened as one flat piece.

Thinking cooling undoes everything

“If we put the toast in the fridge it will be bread again”

Try this: Test it. Cool the toast and compare it with plain bread. Toasting made something new, so cooling cannot change it back.

Where 2-PS1-4 Fits

Comes BeforeK-PS3-1Observe that sunlight warms the ground, an early look at heat changing materials.
Alongside2-ESS2-3Find where water on Earth is solid ice or liquid, another change caused by temperature.W.2.1Write an opinion with reasons, the same claim-and-evidence move students use here.
Comes Next5-PS1-4Mix substances to see when a brand new substance forms, the idea behind changes that cannot be undone.

Practice 2-PS1-4

Quick Check

  1. An ice pop melts on a hot day. Can that change be undone?
  2. Can a cooked egg turn back into a runny egg if you cool it?
  3. What evidence shows a change can be undone?

2-PS1-4: Other Names

2-PS1-4NGSS 2-PS1-4Reversible and irreversible changesHeating and cooling

Official wording from NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. The plain-English lines and everything else on this page are EMStudio’s own explanations, written beside the official wording. They are not part of the standards.

*NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.