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CBSE Class 9 Chemistry Notes for Chapter 1 Matter in our Surroundings

Matter is made up of particles which are so small that they cannot be seen by the naked eye.


  • Particles of matter have space between them.
  • The particles are continuously moving.
  • The particles attract each other.

There are three different states of matter: solid, liquid and gas.

  • Solid state: Solids have definite shape, distinct boundaries, fixed volume and negligible compressibility. The particles in solids are tightly packed.
  • Liquid state: Liquids have no fixed shape but have fixed volume. Solids, liquids and gases can diffuse into liquids. The particles in a liquid have greater space between them as compared to the space between particles in solids.
  • Gaseous state: Gases have no fixed shape. They can be highly compressed quite easily. The particles in a gas have a large space between them.

When the temperature of solids increases, the kinetic energy of the particles increases. Due to this increase in kinetic energy, the particles start vibrating faster. Once the energy supplied overcomes the force of attraction between the particles, they start moving freely. This is when the solid starts converting into liquid. On further heating the liquid then converts into gas.

Latent heat of vaporization is the heat energy required to change 1 kg of liquid into gas atmospheric pressure at the boiling point without changing its temperature.
Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point without any change in the temperature.


  • Solid to liquid is called fusion.
  • Solid to gas and gas to solid is called sublimation.
  • Liquid to solid is called solidification.
  • Liquid to gas is called evaporation.
  • Gas to liquid is called condensation.


  • Evaporation is liquid changing into gaseous state.
  • Evaporation is a surface phenomenon. Increase in surface area means increase in the rate of evaporation.
  • With increase in temperature, evaporation also increases.
  • If the humidity in air is high, evaporation will be less whereas less humidity means more evaporation.
  • If the wind speed is high, evaporation increases.
  • Evaporation causes cooling as the liquid particles have to absorb energy from the surroundings to regain the energy lost in evaporation. This makes the surroundings cold.

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