Schooling · Class 7 · Science · Changes Around Us: Physical and Chemical · Chapter on a page
CBSE Class 7 · Science · NCERT Curiosity
Changes Around Us: Physical and Chemical: chapter on a page
A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).
About the notes: Written by Shishya's AI on 26 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.
This note's current text has no applied fact-check on record.
Mind map
Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.
The mind map as a list
- Key ideas
- physical change
- chemical change
- Physical changes are usually…
- Chemical changes are usually…
- Signs of a chemical change include
- A change of state (solid to liquid…
- Rusting of iron is a chemical…
- Formulas and facts
- Physical change
- Chemical change
- Reversible change
- Irreversible change
- Rusting
- Burning
- Curdling of milk
- Watch out for
- Thinking melting is a chemical change
- Believing all irreversible changes…
- Confusing dissolving with a chemical…
- Thinking burning and melting are the…
- Assuming colour change always means…
What this chapter is about
Every day, things around us change. Ice melts into water. A matchstick burns. Milk turns into curd. Some changes are easy to reverse, while others are not. This chapter helps you understand the difference between physical changes and chemical changes.
Key ideas
- A physical change is a change in the form, size, shape or state of a substance. The substance remains the same. No new substance is formed.
- A chemical change is a change where one or more new substances are formed. The original substance cannot be easily recovered.
- Physical changes are usually reversible. For example, water can freeze into ice and ice can melt back into water.
- Chemical changes are usually irreversible. For example, once paper burns, you cannot get the paper back.
- Signs of a chemical change include: release of heat or light, change in colour, formation of gas bubbles, or formation of a solid from liquids.
- A change of state (solid to liquid to gas) is a physical change because no new substance is created.
- Rusting of iron is a chemical change. Iron combines with oxygen and moisture to form iron oxide, which is a new substance.
- Dissolving sugar in water is a physical change. The sugar is still sugar; it has just spread into the water.
Formulas and facts to remember
- Physical change: Only appearance or state changes; substance stays the same.
- Chemical change: A new substance with new properties is formed.
- Reversible change: A change that can be undone easily. Example: melting of wax.
- Irreversible change: A change that cannot be undone easily. Example: cooking an egg.
- Rusting: Iron + Oxygen + Water → Iron oxide (rust). This is a chemical change.
- Burning: When something burns, it combines with oxygen. New substances like ash and gases form.
- Curdling of milk: Adding lemon juice or curd to milk causes a chemical change. The milk becomes curd.
- Cutting or tearing: Cutting paper or cloth is a physical change because no new substance forms.
Common mistakes
- Thinking melting is a chemical change → Melting only changes state; the substance stays the same, so it is physical.
- Believing all irreversible changes are chemical → Some physical changes are also hard to reverse, like breaking a glass, but no new substance forms.
- Confusing dissolving with a chemical reaction → Dissolving salt or sugar in water is physical; the salt or sugar can be recovered by evaporation.
- Thinking burning and melting are the same → Burning creates new substances; melting only changes state.
- Assuming colour change always means chemical change → Sometimes colour changes are physical, like mixing paints, but often colour change does signal a chemical change.
Quick revision
- Physical change: same substance, different form or state.
- Chemical change: new substance formed with new properties.
- Melting, freezing, dissolving and tearing are physical changes.
- Burning, rusting and curdling are chemical changes.
- Look for heat, light, gas bubbles or colour change to spot chemical changes.
- Reversible usually means physical; irreversible usually means chemical.