Combustion and flame is a chapter in class 8 NCERT science book. In NCERT this chapter is marked as chapter number 6. This chapter explains the phenomenon of combustion and things that revolves around this concept. If you were looking for NCERT back exercise Solutions for Combustion and Flame chapter, then you are at the right place.
Combustion and Flame NCERT Solutions Class 8
List the conditions under which combustion can take place
Ans 1: The conditions under which combustion can take place are as follows:-
- A substance for combustion
- Ignition temperature should be reached to attain combustion of the substance
- Presence of oxygen for combustion of the substance
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Question 2: Fill in the blanks:
(a)Burning of wood and coal causes _______ of air.
Ans a) Burning of wood and coal causes pollution of air
(b) A Liquid fuel used in homes is ________
Ans (b) Kerosene oil
(c) Fuel must be heated to its _______ before it starts burning.
Ans (c) ignition temperature
(d) Fire produced by oil cannot be controlled by _______
(d) water
Question 3: Explain how the use of CNG in automobiles has reduced pollution in our cities
The use of CNG in place of petrol and diesel reduce pollutions in the following ways:
(i) CNG is a cleaner fuel so it produces less pollution.
(ii) Less amount of CO2 gas is released on burning of CNG.
(iii) It does not leave any kind of residue after combustion process like other fuels.
Question 4: Compare LPG and wood as fuel
Ans 4:
LPG
1) LPG has high calorific value than wood
2)It occupies less space and can be stored in the cylinders
3) LPG produces pollution on burning like wood does.
Wood
1) Wood has low calorific value.
2) When wood is burnt a large amount of smoke may be produced.
3) Wood needs more labour to be used and needs more space for storage.
Question 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.
Ans. (a) Water is not used to control fires because water can conduct electricity through it. The persons around can get the shocks.
(b) Wood produces a lot of smoke when it is burnt. LPG is a cleaner fuel and is easy to store and carry. So, LPG is a better fuel.
(c) Paper can easily catch fire because it has very low ignition temperature. When this paper is wrapped around an aluminium pipe, the heat gets absorbed by the aluminium metal and the result is that paper does not burn.
Q.7. Name the unit in which the calorific value of a fuel is expressed.
Ans 7. The calorific value of a fuel is expressed in Kilojoules/ kg (kJ/ kg)
Q.8. Explain how CO2 is able to control fires.
- Ans. (i) CO2 is considered as a good fire extinguisher. Fire needs oxygen. CO2 forms a layer and cuts the supply of air.
- (ii) This gas reduces the temperature so the fire can be controlled.
- (iii) You can easily notice CO2 fire extinguishers in schools, colleges and offices
Q.9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Ans. Green leaves have moisture in them so it takes time to reach the ignition temperature but dry leaves can catch fire easily because ignition temperature reaches faster and they catch fire.
Q.10. Which zone of a flame does a goldsmith use for melting gold and silver and why?
Ans. The outermost zone of the candle is the flame is hottest so it is used to melt gold and silver objects.
Q.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.
Ans. Given mass of the fuel = 4.5 kg
Heat released in Joules = 180,000 kJ
Heat released when 1 kg of fuel is burnt =
180,000 kJ/4.5 kg >> 40,000 kJ/kg.
Hence, the calorific value of the fuel will be
40,000 kJ/ Kg.
Q.12. Can the process of rusting be called combustion? Discuss.
Ans: In rusting a layer is formed on the surface of iron objects. No substance is burnt, no heat, and light are released. We can not call it combustion.
Q.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?
Ans. In this experiment, the water kept by Ramesh will be heated faster as it is in the hottest zone of flame that is the outermost zone. Abida’s beaker may take time to heat up.
So, these were the Class 8 Science NCERT Solutions for Chapter 6 Combustion and Flame. Hope you found them useful. Want more NCERT solutions for Maths, English, and Science?? Don’t forget to subscribe to Careeradvice4u. This was Deepak Kumar here. If you have any queries, feel free to ask me through the comments section below.
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