Class IX SEBA Science – Chapter 1: Matter in Our Surroundings
Class IX SEBA Science – Chapter 1: Matter in Our Surroundings
🧪 1. Physical Nature of Matter
- Matter is made up of particles that are extremely small and invisible to the naked eye.
- These particles have space between them (inter-particle space).
- Particles of matter are constantly moving (they have kinetic energy).
- Particles of different substances have different forces of attraction between them.
🌫️ 2. Characteristics of Particles of Matter
- Particles are continuously moving — this motion increases with temperature.
- Particles attract each other — the strength of attraction varies across solids, liquids, and gases.
- Particles have space between them — gases have the most, solids the least.
🧊 3. States of Matter
- Matter exists in three main states — solid, liquid, and gas.
- Solids: Definite shape and volume, tightly packed particles.
- Liquids: No fixed shape, but fixed volume; moderate particle attraction.
- Gases: No fixed shape or volume; particles far apart with negligible attraction.
🔄 4. Can Matter Change Its State?
- Matter can change from one state to another on heating or cooling.
- Melting: Solid to liquid (e.g., ice to water).
- Boiling: Liquid to gas (e.g., water to steam).
- Condensation: Gas to liquid.
- Freezing: Liquid to solid.
- Sublimation: Solid directly to gas (e.g., camphor).
🌡️ 5. Evaporation
- Evaporation is the process of liquid changing into vapor at any temperature below boiling point.
- Factors affecting evaporation:
- Surface area (more area = more evaporation)
- Temperature (higher = faster evaporation)
- Wind speed (higher = faster evaporation)
- Humidity (more humidity = slower evaporation)
- Evaporation causes cooling (e.g., sweating cools our body).
📘 Exercise Questions and Answers
1. Convert the following temperatures to Celsius scale:
a) 300 K = 27°C
b) 573 K = 300°C
2. Convert the following temperatures to Kelvin scale:
a) 25°C = 298 K
b) 373°C = 646 K
3. Give reasons for the following observations:
a) Naphthalene balls disappear with time without leaving any solid → Due to sublimation (solid directly changes into gas).
b) We can get smell of perfume from distance → Due to diffusion of gas particles into air, which travel from high to low concentration.
4. Arrange the following substances in increasing order of forces of attraction:
Water, sugar, oxygen → Oxygen < Water < Sugar
5. What is the physical state of water at:
a) 25°C → Liquid
b) 0°C → Both solid and liquid
c) 100°C → Both liquid and gas
6. Give two reasons to justify:
a) Water is a liquid → Has fixed volume but no fixed shape; can flow.
b) An iron almirah is solid → Has fixed shape and volume; particles are tightly packed.
7. Why is ice at 273 K more effective in cooling than water at the same temperature?
- Ice requires latent heat of fusion to melt, which it absorbs from the surroundings, providing additional cooling.
8. What produces more severe burns: boiling water or steam? Why?
- Steam causes more severe burns than boiling water because it contains more heat energy (latent heat of vaporization).
✍️ Extra Important Questions with Answers
1. What is diffusion? Give an example.
Diffusion is the movement of particles from high concentration to low concentration.
Example: Smell of perfume spreading in a room.
2. Define latent heat.
Latent heat is the amount of heat required to change the state of a unit mass of a substance without changing its temperature.
3. What is melting point?
Melting point is the temperature at which a solid changes into a liquid at atmospheric pressure.
4. Why do solids have a fixed shape?
Because particles in solids are tightly packed and cannot move freely, they have a fixed shape.
5. Why do we feel cold when sweat evaporates?
Sweat absorbs heat from our skin to evaporate, causing cooling effect.
continue to Chapter 2 next?
