CBSE Class 9 Science Quick Review Chapter Wise

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Characteristics of particles :
(i) Large number of particles constitute matter.
(ii) Particles of matter are very small in size.
(iii) Particles of matter have spaces between them.
(iv) Particles of matter are continuously in motion.
(v) Particles of matter attract each other.

Matter around us exists in three states-solid, liquid and gas.

Know the Terms

• Humidity : The amount of water vapour present in the air.
  

• Density : It is the mass occupied by a solid per unit volume and is obtained by dividing the mass of a particular solid by the volume occupied.
  

• Fusion : The process in which a solid changes to liquid state by absorbing heat at constant temperature.
  

• Diffusion : The process in which particles of one substance occupy the vacant spaces present in the particles of the other substance, is called diffusion.
  

• Condensation : The process in which a gas changes into liquid state by giving out heat at constant temperature.
  

• Latent heat : The hidden heat which breaks the force of attraction between the molecules during change of state.
  

• Latent heat of fusion : The amount of heat energy that is needed to convert one kg of a solid into the liquid state at atmospheric pressure at its melting point is termed as latent heat of fusion.
  

• Boiling point : The temperature at which a liquid starts boiling at the atmospheric pressure is known as boiling point.
  

• Freezing point : The temperature at which a liquid changes to solid by giving out heat at the atmospheric pressure.
  

• Latent heat of vaporization : The amount of heat energy that is needed to convert one kg of a liquid at its boiling point temperature into its vapour state without any rise in temperature, is termed as latent heat of vaporization.
  

• Melting point : The melting point of a solid may be defined as the temperature at which a solid melts to become a liquid at the atmospheric pressure.
  

• Sublimation : Sublimation is the change of a solid directly into the gaseous state without passing through the liquid state upon heating and back to the solid state when the temperature is lowered.
  

• Evaporation : The phenomenon of change of liquid to the vapour state at any temperature below the boiling point of the liquid is termed as evaporation.
  

• Transpiration : The process of evaporation of water from the aerial parts of plants especially leaves is called transpiration.
  

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