Physical and Chemical Changes
Physical changes alter form; chemical changes create new substances.
About this topic
A physical change alters the form or appearance of a substance without making a new one: melting ice, dissolving sugar or crushing a can. A chemical change produces new substances with different properties, such as burning wood, rusting iron or baking a cake.
Signs of a chemical change include gas bubbles, a colour change, a precipitate, light or heat released, and a new smell. These are clues, not proof: boiling water makes bubbles and heat is absorbed, yet it stays water. The real test is whether the particles have been rearranged into different substances, with bonds broken and formed. Chemical changes are usually hard to reverse, while many physical changes can be undone by cooling, evaporating or filtering.
Consider an iron nail. Bending it is physical, since it is still iron. Leaving it in damp air so that it turns into flaky orange rust is chemical, because iron and oxygen have formed iron oxide, a new compound with different properties. In the kitchen, melting butter is physical but frying an egg is chemical, since the proteins change permanently.
Students often say that dissolving is chemical because the solid seems to disappear. Sugar in water can be recovered by evaporation, so it is physical. Also remember that mass is conserved in both kinds of change.
Key ideas
- Melting and cutting are physical
- Burning and rusting are chemical
- Signs: gas, colour change, heat, precipitate
Quick check
Use cases: where Physical and Chemical Changes helps
- Homework: review the key idea behind Physical and Chemical Changes before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Physical and Chemical Changes without notes.
- Visual learning: play with the interactive lab to see how Physical and Chemical Changes changes when you adjust its inputs.
- Teaching a friend: explain Physical and Chemical Changes in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Physical and Chemical Changes?
Physical changes alter form; chemical changes create new substances.
What will I learn in Physical and Chemical Changes?
Melting and cutting are physical. Burning and rusting are chemical. Signs: gas, colour change, heat, precipitate.
Is Physical and Chemical Changes part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Physical and Chemical Changes lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Physical and Chemical Changes?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.