CBSE Class 7 · Science
Changes Around Us: Physical and Chemical
Official NCERT chapter from Curiosity (book code gecu1). ExamMaster notes are original teaching at CBSE Class 7 depth.
This lesson follows the official chapter “Changes Around Us: Physical and Chemical” in Curiosity. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.
- CBSE Class 7
- Easy level
- 8 concepts
1A Substance May Change in Appearance but Remain the Same!
A physical change can alter look or form while the substance-word stays: ice to water, tearing paper, dissolving as taught when you can get the solid back. Same stuff, new appearance.
A melted ice cube that you call “a new chemical” is the miss of this heading.
Figure. Ice can become a puddle and still be H₂O. Appearance changed; the substance did not. That is a physical change — melting, not a new material.
How it works
- Name the start substanceIce, or paper.
- Name the look-changeMelt, tear, dissolve-as-taught.
- Ask if you still have the same substance-wordPhysical if yes.
2A Substance May Change in Appearance and Not Remain the Same
A chemical change makes a new substance you can argue: rust from iron, a gas from a taught mix, a cooked change you were shown. Appearance changes and the substance-word does not stay.
A torn paper is not a new substance.
Figure. Burnt paper is not paper in a new shape. Ash and gas are new substances. Appearance changed and the stuff did not remain the same — a chemical change.
How it works
- Name the startIron, or the mix you were given.
- Name a new stuff you can point toRust, a gas, a cooked product as taught.
- Call it chemical if the new stuff is the pointNot just a new shape.
3Some Other Processes Involving Chemical Changes
Other chemical processes you were shown (burning, a gas-on-limewater if that was the lesson, rusting again) still need a new-substance argument. The heading is “some other processes”, not a new theory.
A list of names without one pointed product is a poster.
Figure. Other chemical changes make a new substance too: iron becomes rust, fuel becomes ash, and a leaf builds sugar from CO₂. Each ends with stuff you did not start with.
How it works
- Pick one taught processThis one.
- Name the new substance or the taught signThe product.
- Keep it as another chemical caseSame test, new example.
4Can Physical and Chemical Changes Occur Together?
Yes: a change can have both jobs — ice melts (physical) while something else reacts (chemical), or a taught mix that dissolves and then reacts. Name each job; do not pick a favourite word for the whole event.
Calling the whole kitchen “chemical” because something browned is a blur.
Figure. A burning candle does both at once. Wax melts — same substance, a physical change. Wax also burns to new gases — a chemical change. One object, two kinds of change.
How it works
- Split the event into jobsThis melt, that brown.
- Tag each job physical or chemicalTwo tags allowed.
- Keep both if both tests passedTogether.
5Are Changes Permanent?
Permanent here means you cannot reasonably get the start back by a simple reverse you were taught. Ice can freeze again; rust is not a quick undo in class. Permanent is a practical word, not forever-in-the-universe.
A torn paper you could tape is a weak “permanent”.
Figure. Not every change is permanent. Ice and water can swap back by a reverse step. Paper to ash cannot — cooling the ash does not grow a page. Permanent means no simple reverse, not 'it lasted a long time'.
How it works
- Ask if a simple reverse was taughtFreeze, evaporate, unmix.
- If yes and it works, the change was not permanent in that senseGet-back.
- If the new substance stays, call it lasting for this classPractical permanent.
6Are All Changes Desirable?
Desirable is a use-word: rust on a tool is usually not wanted; cooking a food change may be wanted. Science names the change; desirable is the job we asked for. They are different columns.
A dangerous mix is not “good science” because it was chemical.
Figure. A change can be real and still unwelcome. Cooking and ripening are desirable. Rust and spoilage are the same kind of change aimed at the wrong stuff. Desirable is a human verdict, not the test for chemical.
How it works
- Name the changeScience column.
- Name the job we wantedUse column.
- Say desirable only in the use columnNot a property-test.
7Some Slow Natural Changes
Slow natural changes take a wait you can name: rust, a fruit ripening as taught, rock-wear if that was the lesson. Slow is not “never”. A one-period look may miss them — the heading is a patience-note.
A change you did not wait for is not proven slow; you just did not see it.
Figure. Some natural changes are slow. A nail stays iron for a long time, then dulls, then rusts. Weathering a rock and ripening fruit are the same idea: a new look that took months, not a minute.
How it works
- Name a taught slow changeRust, ripen…
- Name that a short look can miss itPatience.
- Keep one caseNot every mountain today.
8A definition is a test you can run
Physical versus chemical is a test: same substance-word, or a new one you can point to. If you cannot run that question, you do not yet have the pair.
A heading “changes around us” with no test is a poster.
Figure. A definition is a test you can run. Same cup, same spoon, same water: only the solid changes. Sugar disappears into the water; sand stays as bits. Record what happened, not what you hoped.
How it works
- Ask same-substance or new-substanceThe test.
- Point to the evidenceMelt-back, or rust.
- Then tag the changeThe definition ran.
Ice melting is
- Physical — same substance-word, new form
- Chemical — a new substance called water-from-nowhere
- A circuit
Water is still water.
Notes
- Mapped to the official NCERT chapter “Changes Around Us: Physical and Chemical”. Original teaching only — no textbook sentences.
- Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.
Recap
Hold these pegs from the official chapter “Changes Around Us: Physical and Chemical”. The wording is ExamMaster’s teaching, not a textbook recap.
- A Substance May Change in Appearance but Remain the Same!
- A physical change can alter look or form while the substance-word stays: ice to water, tearing paper, dissolving as taught when you can get the solid back.
- A Substance May Change in Appearance and Not Remain the Same
- A chemical change makes a new substance you can argue: rust from iron, a gas from a taught mix, a cooked change you were shown.
- Some Other Processes Involving Chemical Changes
- Other chemical processes you were shown (burning, a gas-on-limewater if that was the lesson, rusting again) still need a new-substance argument.
- Can Physical and Chemical Changes Occur Together?
- Yes: a change can have both jobs — ice melts (physical) while something else reacts (chemical), or a taught mix that dissolves and then reacts.
- Are Changes Permanent?
- Permanent here means you cannot reasonably get the start back by a simple reverse you were taught.
- Are All Changes Desirable?
- Desirable is a use-word: rust on a tool is usually not wanted; cooking a food change may be wanted.
Practise Changes Around Us: Physical and Chemical
Reading is free and needs no account. Practice, mocks and progress live in the app.
- A 4-question practice set that ends the chapter
- 1 quick check with worked explanations
- Timed mocks scored with the real marking scheme
- Readiness tracked per topic, kept on your device