Combustion and Flame


Explain how C02 is able to control fires.


C02 is a non-combustible gas and extinguishes fire in two ways: (i) Since it is heavier than oxygen, it covers the fire like a blanket and cuts off the contact between oxygen and fuel. (ii) In cylinders, C02 is kept in the liquid form. When released, it expands enormously and cools down. This brings down the temperature of the fuel, which helps in controlling the fire.

Combustion and Flame

Q 1.

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?

Q 2.

List conditions under which combustion can take place.

Q 3.

Compare LPG and wood as fuels.

Q 4.

Explain how C02 is able to control fires.

Q 5.

It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Q 6.

Make a labelled diagram of a candle flame.

Q 7.

Explain how the use of CNG in automobiles has reduced pollution in our cities.

Q 8.

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.

Q 9.

Can the process of rusting be called combustion? Discuss.

Q 10.

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.

Q 11.

Name the unit in which the calorific value of a fuel is expressed.

Q 12.

Which zone of a flame does a goldsmith use for melting gold and silver and why?