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๐ฌ Think about it
Open a bottle of perfume and soon the whole room smells of it. Gas spreads everywhere and fills all the space it can. Its particles are completely free, like kids running in an open playground. Let's watch how gases behave.
Do gases have a fixed shape or volume?
- A gas spreads to fill the entire available space.
- So gases do not have a fixed volume.
- Like liquids, they take the shape of their container.
- Gas particles move freely in all directions.
Example:
Smoke from an incense stick fills a whole jar, taking up all the space.
In this Activity, we will use smoke to show that a gas spreads to fill all the space available to it.
Safety first
Be careful while burning an incense stick. If using iodine instead, be careful — iodine vapours can cause irritation.
Materials needed
Two transparent gas jars or glass tumblers, an incense stick, a glass plate (optionally solid iodine).
Procedure
1. Take two transparent gas jars and mark them A and B.
2. Create some smoke by burning an incense stick.
3. Hold Gas Jar A upside down over the smoke so it traps the smoke inside.
4. Turn it over and cover it with a glass plate.
5. Hold Gas Jar B upside down and place it over the glass plate covering Jar A.
6. Remove the glass plate slowly, keeping the jars close with no gap.
7. Observe how the smoke spreads into Gas Jar B.
2. Create some smoke by burning an incense stick.
3. Hold Gas Jar A upside down over the smoke so it traps the smoke inside.
4. Turn it over and cover it with a glass plate.
5. Hold Gas Jar B upside down and place it over the glass plate covering Jar A.
6. Remove the glass plate slowly, keeping the jars close with no gap.
7. Observe how the smoke spreads into Gas Jar B.
Observation
The smoke fills the entire space in Gas Jar B, spreading from Jar A.
Explanation
Gas particles move freely in all directions and interparticle attractions are negligible. So gases have no fixed shape or volume and fill all the available space. The smoke particles, hit by invisible gas particles, let us see this motion. The same can be shown using iodine vapour.
โ Summary
- Smoke trapped in jar
- Plate removed
- Smoke fills both jars
- No fixed volume
Important Points
- Gas particles move freely; attractions are negligible.
- Gases have no fixed shape or volume and fill all space.
- Liquids and gases both flow, so they are fluids.
Important Definitions
- Gaseous state — the state where particles move freely in all directions with negligible attraction, having no fixed shape or volume.
๐ NCERT Question 4 — Why do gases mix
Why do gases mix easily with each other, while solids do not?
View Answer →
