📘 Chapter 1: Matter in Our Surroundings – Full Explanation (CBSE Class 9 Science)
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I. What is Matter?
- Matter: Anything that has mass and occupies space.
- Examples: Water, air, books, clothes, soil.
- Not considered matter: Love, thoughts, feelings (they don’t occupy space or have mass).
🔹 II. Early Classifications of Matter
- Ancient Indian philosophers described matter as made up of Panch Tatva:
- Air (Vayu)
- Water (Jal)
- Fire (Agni)
- Earth (Prithvi)
- Sky/Space (Akash)
- Modern science classifies matter based on physical state and chemical composition.
🔹 III. Physical Nature of Matter
1. Particles of matter are very small.
- They are so small they cannot be seen by naked eyes.
- Eg: A crystal of potassium permanganate can color a large volume of water.
2. Particles have space between them.
- More space in gases than liquids; least in solids.
3. Particles are constantly moving.
- Movement increases with temperature (Brownian motion).
4. Particles attract each other.
- The force of attraction is strongest in solids, weaker in liquids, and weakest in gases.
🔹 IV. States of Matter (with Real-Life Examples)
🧱 1. Solid
- Fixed shape and volume
- Rigid, incompressible
- Examples: Ice, wood, stone
💧 2. Liquid
- No fixed shape, fixed volume
- Can flow (fluid), less compressible
- Examples: Water, milk, alcohol
🌫️ 3. Gas
- No fixed shape or volume
- Highly compressible, flows easily
- Examples: Air, oxygen, carbon dioxide
🔄 New Research: Scientists have discovered two more states—Plasma and Bose-Einstein Condensate (BEC).
🔹 V. Interconversion of States of Matter
Matter can change from one state to another by:
- Changing temperature
- Changing pressure
| Process | Change |
| Melting | Solid → Liquid |
| Freezing | Liquid → Solid |
| Vaporization | Liquid → Gas |
| Condensation | Gas → Liquid |
| Sublimation | Solid ↔ Gas (e.g. Camphor) |
| Deposition | Gas → Solid |
🌡️ Latent Heat
- Latent Heat of Fusion: Heat required to convert solid to liquid without change in temperature.
- Latent Heat of Vaporization: Heat required to convert liquid to gas without temperature change.
🔹 VI. Sublimation
- Definition: Direct conversion of solid to gas and vice versa.
- Examples: Camphor, iodine, ammonium chloride, dry ice (solid CO₂)
🔹 VII. Evaporation (Detailed)
Evaporation is the surface phenomenon of liquid changing into vapor below boiling point.
🧪 Factors Affecting Evaporation:
| Factor | Effect |
| Surface Area | ↑ Surface → ↑ Evaporation rate |
| Temperature | ↑ Temperature → ↑ Kinetic energy |
| Humidity | ↓ Humidity → ↑ Evaporation |
| Wind Speed | ↑ Wind → Removes vapor → ↑ Evaporation |
🌬️ Applications:
- Sweat cools body via evaporation.
- Clothes dry faster on windy days.
- Water kept in earthen pots feels cool.
🔹 VIII. Boiling vs Evaporation
| Property | Boiling | Evaporation |
| Temperature | At boiling point only | At any temperature |
| Process | Bulk (entire liquid) | Surface phenomenon |
| Energy | Requires external heat | Takes heat from surroundings |
| Speed | Fast | Slow |
🔹 IX. Plasma & Bose-Einstein Condensate (Extra Knowledge)
⚡ Plasma:
- Ionized gas with free electrons
- Found in: Sun, stars, neon signs
❄️ Bose-Einstein Condensate (BEC):
- Discovered by: Satyendra Nath Bose & Einstein
- Super-cooled atoms behaving as a single quantum entity
🔹 X. Diagram Summary (Suggested Drawings)
- States of Matter:
- Solid (compact particles), Liquid (loosely packed), Gas (very loose)
- Evaporation Process:
- Surface molecules escaping into vapor
- Graph: Heating Curve of Ice to Steam
- Interconversion Flowchart:
- All six processes
🔹 XI. NCERT Exercises (Selected Questions with Key Points)
🔸 Q1: Convert the following temperature to Celsius:
- 300 K = 27°C
- 573 K = 300°C
🔸 Q2: Why does a desert cooler cool better on a hot dry day?
- Because dry air has low humidity → more evaporation → better cooling.
🔸 Q3: Why do we feel cool when sweat evaporates?
- Evaporation takes heat from our body, causing cooling.
🔸 Q4: Why should we wear cotton clothes in summer?
- Cotton absorbs sweat and facilitates evaporation, keeping us cool.
🔹 XII. HOTS (Higher Order Thinking Skills)
- Why does a gas fill the container completely?
- Because gas particles move freely in all directions.
- Can a liquid have a fixed shape?
- No, but it takes the shape of the container due to weaker intermolecular force.
- Why is solid CO₂ called dry ice?
- Because it sublimates directly into gas without becoming liquid.
🔹 XIII. Mind Map
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MATTER
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Physical Nature States of Matter
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Particles -> tiny, moving Solid, Liquid, Gas
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Properties Interconversion
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Evaporation, Latent Heat Melting, Boiling…
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