Combustion and Flame - Worksheets

CBSE Worksheet-01
Class–VIII (Combustion and Flame)

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1. Combustion refers to a:-
   1. physical change
   2. chemical change
   3. cyclic change
   4. all the above
2. Select the combustible substance: -
   1. wax
   2. water
   3. glass
   4. sand
3. During combustion of coal, the supporter of combustion is:-
   1. hydrogen
   2. nitrogen
   3. oxygen
   4. carbon dioxide
4. Fire can be extinguished by :-
   1. lowering temperature below ignition temperature
   2. cutting the supply of oxygen
   3. removing non combustible substances from surroundings
   4. both a & b
5. Match the column :-

   a. Incomplete combustion	i) Burning a firecracker
   b. Explosion	ii) carbon to carbon monoxide
   c. Calorific value	iii) carbon to carbon dioxide
   d. Complete combustion	iv) spontaneous
   e. Slow combustion	v) fuel efficiency

6. Fill in the blanks:-
   1. The lowest temperature at which any substance catches fire is called ______ temperature.
   2. The substances which burn in air are called ______ substances.
   3. In the absence of sufficient ______ , combustion of a fuel remains incomplete.
   4. ______ should not be used for extinguishing fire caused by an electric short-circuit.
   5. The middle zone of a candle flame is also called the zone of ______ combustion.
7. How will you distinguish between fire extinguishing action of water and CO2 ?
8. Define fuel efficiency?
9. If you find such a symbol/sign on a box etc, what does it represent?
   
10. Write the correct words by putting letters in correct sequence-i) tiningoi ii) submobticle
11. Write the harmful effects on the environment due to burning of fuels?

CBSE Worksheet-01
Class–VIII (Combustion and Flame)
[Answer]

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1. b
2. a
3. c
4. d
5. a. -ii, b.- i, c.- v, d.- iii, e.- iv.
6. a. ignition b. combustible c. oxygen d. water e. partial / incomplete.
7. Water helps to extinguish fire in two ways:-
   1. It brings temperature of the combustible material below its ignition temperature and the water vapour formed due to the heat of fire cuts the supply of oxygen.
   2. Carbon dioxide is highly volatile. So, it immediately vaporises to cut off the supply of air. In the absence of supporter of combustion, fire is extinguished.
8. Different types of fuels generate different amounts of heat. The heat produced by fuels is measured and expressed through its calorific value. For a fuel to be categorised as a good fuel should have a high calorific value, in other words greater is the calorific value larger is amount of heat produced on burning that fuel and vice a versa.
9. It represents that the substance kept inside the box is inflammable.
10. 1. ignition
    2. combustible
11. Harmful effects on the environment due to burning of fuels :-
    1. Fuels like wood, coal, petroleum release unburnt carbon particles which cause respiratory diseases like asthma.
    2. Incomplete combustion of fuels release carbon monoxide gas which is a very poisonous gas which can cause death.
    3. Burning of most fuels release carbon dioxide gas which causes rise in the temperature of the atmosphere. This is called global warming. It causes melting of polar ice, rise in sea level and flooding of coastal areas.
    4. Burning of coal and petroleum release oxides of sulphur and nitrogen which dissolve in rain water and forms acid rain. It is harmful for crops, soil and damages buildings.