---
title: "Physical vs Chemical Changes"
description: "Distinguish between physical changes (reversible, no new substances formed) and chemical changes (new substances formed, often irreversible), using conservation of mass to understand both types"
canonical: https://lightmysky.com/learn/science/physical-vs-chemical-changes-mt_1hgck6ucII
source: https://lightmysky.com/learn/science/physical-vs-chemical-changes-mt_1hgck6ucII.md
retrieved: 2026-10-19
---

> **Agent view.** This is the Markdown twin of the page, for tools and assistants.
> When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md
> API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md
> Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt
> Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json
> Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`.

# Physical vs Chemical Changes

Distinguish between physical changes (reversible, no new substances formed) and chemical changes (new substances formed, often irreversible), using conservation of mass to understand both types

Subject: Science · Area: Matter & Materials · Ages 11 to 13
Page: https://lightmysky.com/learn/science/physical-vs-chemical-changes-mt_1hgck6ucII

## Ready when they can

- Classifies given changes as physical or chemical with justification
- Explains what conservation of mass means and why mass is conserved in chemical reactions
- Names observable signs that a chemical reaction has occurred (colour change, gas produced, temperature change, precipitate)
- Explains why dissolving is a physical change but burning is a chemical change

## Lesson: Physical vs chemical changes

Some changes just change how something looks. Other changes turn a substance into something brand new. A physical change keeps the same substance. A chemical change makes a new substance. In a chemical change the atoms rearrange into new substances. No atoms are made or lost, so the total mass stays the same. If a gas drifts away, or oxygen from the air joins in, you have to count it too.

**Example.** Dissolve sugar in your tea and it seems to disappear, but it's still sugar. Let the water evaporate and you'd get the sugar back. That's a physical change. Now burn toast in the toaster. The bread reacts with oxygen and turns into ash, smoke, and gases. You can never turn that ash back into bread. That's a chemical change.

*(drawing: Burning 20 g of wood uses about 30 g of oxygen from the air. Afterwards there is 1 g of ash and 49 g of gases that drift away. That is 50 g before and 50 g after.)*

Look for these signs that a chemical change might be happening: a colour change, gas bubbles, a sudden temperature change, or a new solid forming in a liquid (called a precipitate). One sign is a good clue, though scientists often check for more than one before they're sure.

**Recap.** Physical changes rearrange the same substance, but chemical changes create new substances, and mass is conserved either way.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [The Particle Model](https://lightmysky.com/learn/science/the-particle-model-mt_b6kZgqolEd)
- [Conservation of Mass](https://lightmysky.com/learn/science/conservation-of-mass-mt_ehC1wsdmUz)
- [Irreversible Changes](https://lightmysky.com/learn/science/irreversible-changes-mt_rbPioPELM1)
- [Reversible Changes](https://lightmysky.com/learn/science/reversible-changes-mt_UKmtuAsSLN)
- [Atoms, Elements & Compounds](https://lightmysky.com/learn/science/atoms-elements-and-compounds-mt_Z_Wu_77ybI)

## Opens up

- [Types of Chemical Reaction](https://lightmysky.com/learn/science/types-of-chemical-reaction-mt_v0K6GRi4ZL)