CBSE Class 9 Science - Chapter 1: Matter in Our Surroundings (Notes)

 

                    CBSE Class 9 Science - 

            Chapter 1: Matter in Our Surroundings (Notes)

Introduction to Matter

• Matter is anything that has mass and occupies space.
• It exists in different forms and can be classified based on its physical and chemical properties.

Physical Nature of Matter

• Matter is made up of tiny particles.
• These particles are very small and cannot be seen with the naked eye.
• They have space between them and are constantly moving.
• Particles of matter attract each other.

States of Matter

Matter exists in three primary states:

1. Solid

   • Definite shape and volume
     
     
     
     
   • Particles are tightly packed
   • Strong intermolecular forces
   • Least kinetic energy
   • Cannot be compressed

2. Liquid

   • No fixed shape but definite volume
   • Particles are loosely packed compared to solids
   • Weaker intermolecular forces than solids
   • Can flow and take the shape of a container
   • Slightly compressible

3. Gas

   • Neither definite shape nor volume
   • Particles are far apart
   • Weak intermolecular forces
   • Highly compressible
   • High kinetic energy

Change of State of Matter

• Matter can change from one state to another by changing temperature or pressure.

Melting (Fusion): Solid → Liquid (by heating)

Melting Point: The temperature at which a solid turns into a liquid.

Boiling (Vaporization): Liquid → Gas (by heating)

Boiling Point: The temperature at which a liquid changes to gas.
Condensation: Gas → Liquid (by cooling)
Freezing (Solidification): Liquid → Solid (by cooling)

Sublimation: Solid → Gas (directly without becoming a liquid)

Example: Camphor, dry ice (solid CO₂).
Deposition: Gas → Solid (directly)

Effects of Change in Temperature and Pressure

• Increasing temperature increases kinetic energy, leading to a change in state.
• Increasing pressure can turn gases into liquids (e.g., LPG and CNG).

Evaporation

• Process where liquid changes into vapor at any temperature below its boiling point.
• Factors Affecting Evaporation:
  • Surface Area: More surface area increases evaporation.
  • Temperature: Higher temperature increases evaporation.
  • Humidity: Higher humidity decreases evaporation.
  • Wind Speed: Higher wind speed increases evaporation.

Latent Heat

• Latent Heat of Fusion: Heat required to convert a solid into liquid without changing temperature.
• Latent Heat of Vaporization: Heat required to convert a liquid into gas without changing temperature.

Importance of Evaporation in Daily Life

• Cooling effect of perspiration (sweating).
• Earthen pots keep water cool.
• Water cools down when sprinkled on the floor during summers.