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SAI International School
                                               Subject - Chemistry
                                                     Class - VIII
                                     Topic – COMBUSTION AND FLAME
                 Sub-Topic- Types of combustion, Calorific Value and Numericals,
                                                        Flame


                                                  LESSON NOTES


       Types of Combustion

       There are three types of combustion to study.

       1.  Rapid combustion.
          The combustion reaction in which a large amount of heat and light are produced in a
          short time is called rapid combustion.
          For example, when we bring a lighted match stick near the burner of a gas stove in the
          kitchen, the cooking gas starts burning at once producing a lot of heat and some light.
       2.  Spontaneous combustion
          The combustion reaction which occurs on its own (without the help of any external heat)
          is called spontaneous combustion. In spontaneous combustion, the substance suddenly
          bursts into flames and starts burning without being heated. It takes place at room
          temperature.
          For example, white phosphorus undergoes spontaneous combustion when it comes in
          contact with air.
       3.  Explosive combustion
          A very fast combustion reaction in which a large amount of heat, light, and sound is
          produced, is called explosive combustion. A large amount of gasses is also released
          quickly. Because of the rapid expansion of these gases explosion occurs.
          For example, the burning of a firecracker.
          Fuels
           A material that is burnt to produce heat is called fuel. Some of the common fuels are
          wood, coal LPG, etc.
          Fuels can be found in all three states.
          Examples of solid fuels are wood, charcoal, coke, etc.
          Liquid fuels are kerosene, petrol, etc.
          Gaseous fuels are natural gas, petroleum gas, biogas, etc.

       Calorific Value
       Different fuels produce different amounts of heat on burning. Some fuels produce more heat
       whereas other fuels produce less heat. The efficiency of a fuel is expressed in terms of its
       calorific value.
       The amount of heat produced by the complete burning (or complete combustion) of 1
       kilogram of a fuel is called its calorific value.
       The calorific value of a fuel is expressed in the unit of ‘kilojoules per kilogram’ or kJ/kg.
       The calorific value of a fuel can be calculated by the given formula,
                         Heat produced on complete combustion of the fuel
       Calorific value =
                                 Total mass of the fuel combusted


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