Gas

Gases

What you'll learn

Gases have no fixed shape or volume — they spread to fill space.
Air is a mixture of gases we breathe.
Gases are often invisible but real (balloon, tyre, bubbles).
Connect to Looking Around 3 — wind, breath, and inflated balls.

Key concepts

Level 1 — Core idea

Verbal: Blow a balloon — air (gas) fills it and pushes the rubber out.

Symbolic: Gas → no fixed shape + no fixed volume.

Visual: Open perfume bottle — smell spreads across the room; gas particles spread.

Level 2 — Going deeper

We cannot see air, but we feel wind and see leaves move. Compressed gas in a balloon has pressure pushing on the walls.

NCERT anchor

NCERT Looking Around 3, Chapter 13 and outdoor activities discuss wind moving things. Chapter 7 links evaporation — water vapour (gas) in air.

Worked example

Why does a flat balloon grow when you blow into it?

Step 1 — Your breath adds **air** (gas) inside
Step 2 — Gas spreads to fill balloon space
Step 3 — Balloon expands → gas has **no fixed volume** ✓

Compare air in a small balloon vs large balloon.

Step 1 — Same air **spreads** to match balloon size
Step 2 — Volume of gas **changes** with container
Step 3 — Gas unlike liquid/solid in this way ✓

Common mistakes

Mistake	Why	Fix
Air is nothing	Invisible = not real	Air is matter with mass
Gas has fixed volume like liquid	Balloon seems fixed	Pop balloon — gas escapes and spreads
Only smoke is gas	Visible gases only	Air is gas though invisible
Steam is liquid	White cloud confusion	Steam is water vapour (gas); mist has tiny drops

Quick check

Give one proof that air exists.
Does gas keep its shape in a box?
Solid, liquid, or gas: oxygen we breathe?
Stretch: Why does a tyre look flat when air leaks out?

Revision tip: Three-state chant: solid — shape+volume; liquid — volume only; gas — neither fixed.

Open the Practice tab for graded questions on Gases.

Gas

Gas