1. List conditions under which combustion can take place.
2. Fill in the blanks:
(a) Burning of wood and coal causes of air. (b) A liquid fuel used in homes is .
(c) Fuel must be heated to its before it starts burning. (d) Fire produced by oil cannot be controlled by .
3. Explain how the use of CNG in automobiles has reduced pollution in our cities.
4. Compare LPG and wood as fuels.
5. Give reasons.
(a) Water is not used to control fires involving electrical equipment.
(b) LPG is a better domestic fuel than wood.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
6. Make a labelled diagram of a candle flame.
7. Name the unit in which the calorific value of a fuel is expressed.
8. Explain how CO2 is able to control fires.
9. It is difficult to burn a heap of green leaves, but dry leaves catch fire easily. Explain.
10. Which zone of a flame does a goldsmith use for melting gold and silver and why?
11. In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.
12. Can the process of rusting be called combustion? Discuss.
13. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time.
1. Below are the three conditions under which combustion can take place:
(a) Presence of a fuel
(b) Presence of Air (oxygen)
(c) Ignition temperature (minimum temperature at which a substance catches fire)
2.
(a) Burning of wood and coal causes pollution of air.
(b) A liquid fuel used in homes is liquefied petroleum gas (LPG). (c) Fuel must be heated to its ignition temperature before it starts
burning.
(d) Fire produced by oil cannot be controlled by water.
3. The amount of unburnt fuel in CNG is very less compared to petroleum. CNG is referred to as a clean fuel, as it does not produce smoke and harmful substances that are produced in petroleum which are harmful to the environment, replacing petroleum with CNG has reduced pollution in our cities.
4. Wood is a fuel which is obtained from trees, producing lot of smoke on combustion, causing respiratory problems. On replacing wood with LPG, Problems in dealing with wood are overcome. LPG is referred to as a clean fuel as it does not
kJ/kg). Hence, LPG is a better fuel than wood.
5.
(a) Water is a good conductor of electricity. If water is used to control fire, the person may be electrocuted and usage of water may damage the equipment.
(b) The smoke and unburnt impurities in the fuel are minute compared to that of wood. The harmful gases evolved in the LPG is in traces to that of wood. Hence, LPG is better fuel than wood.
(c) A piece of paper wrapped around aluminum pipe does not catch fire easily because aluminum is a good conductor of heat. The heat is transferred from paper to aluminum, which does not enable the paper to reach its ignition temperature.
6.
7. The calorific value of a fuel is expressed in kilojoule per kilogram
(kJ/kg).
extinguisher.
(i) CO2 is heavier than oxygen, when released Carbon dioxide acts as a protective blanket, stopping the supply of oxygen to the fuel.
(ii) Carbon dioxide is stored in liquid state. On releasing, it expands and cools down the temperature of the surroundings.
Hence, the fire is controlled.
9. Green leaves have higher moisture content than that of the dry leaves. Hence, it is difficult to burn a heap of green leaves that that of dry leaves.
10. Goldsmiths use outermost zone of the flame to melt gold and silver because the outermost zone is the hottest flame as it undergoes complete combustion.
11. The amount of heat produced when 1 kg of fuel is completely burnt is known as calorific value of the fuel.
Now,
Heat produced by 4.5 kg of fuel = 180000 kJ Therefore, heat produced by
= 40,000 kJ/kg
Hence, the calorific value of the fuel is 40,000 kJ/kg.
12. Yes, the process of rusting can be called as combustion. This is because combustion is a process of reaction of substance with oxygen to liberate heat, light and energy. Whereas rusting is slow reaction of Metal with oxygen liberating energy. Hence, rusting is known as slow combustion.
13. Beaker belonging to Ramesh is heated in shorter time because the outer most part of flame is the hottest flame compared to the yellow part of the flam
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