NCERT Solutions for Class 9 Science Chapter 1 Matter in Our Surroundings

Short Note:

• Matter: Anything that occupies space and has mass is called matter.

• Characteristics of Particles of Matter:

  1. Particles of matter have spaces between them.

  2. Particles of matter are continuously moving (possess kinetic energy).

  3. Particles of matter attract each other due to intermolecular forces.

• Diffusion: The intermixing of particles of two different types of matter on their own.

Short Note:

• Solids: Definite shape, distinct boundaries, fixed volume, high density, negligibly compressible, rigid.

• Liquids: No fixed shape, fixed volume, lower density than solids, fluid, moderate compressibility.

• Gases: No fixed shape or volume, highly compressible, high fluidity, low density, expand to fill containers.

Short Note:

• Melting Point: Temperature at which a solid changes into a liquid at atmospheric pressure.

• Boiling Point: Temperature at which a liquid changes into a gas at atmospheric pressure.

• Latent Heat of Fusion: Amount of heat energy required to change 1 kg of solid into liquid at its melting point.

• Latent Heat of Vaporisation: Amount of heat energy required to change 1 kg of liquid into gas at its boiling point.

• Sublimation: Change of state directly from solid to gas without changing into liquid (e.g., Camphor, Ammonium Chloride).

Short Note:

• Evaporation: Surface phenomenon where a liquid changes into vapor at any temperature below its boiling point.

• Factors Increasing Evaporation:

  1. Increase in surface area.

  2. Increase in temperature.

  3. Increase in wind speed.

  4. Decrease in humidity.

• Cooling Effect: Evaporation causes cooling because high-energy particles escape, absorbing energy from surroundings.