DAV Class 8 Science Solution Chapter 7 Combustion
DAV School Books Class 8 Science Solution Chapter 7 Combustion all Question Answer. DAV Class 8 7th Chapter Combustion full Chapter explanation by expert teacher.
DAV School Books Class 8 Science Solution Chapter 7 Combustion
A.) Fill in the blanks.
1.) A good fuel should have its ignition temperature ___________ the room temperature.
2.) Burning of cowdung cakes is an example of ___________ combustion.
3.) The ___________ zone of a candle flame, is the coldest.
4.) The non-luminous zone of a candle flame is the ___________ part of the flame.
5.) During incomplete combustion of a fuel, ___________ gas is formed.
Answer: (1) above (2) slow (3) innermost (4) hottest/outer most (5) Carbon monoxide
B.) State True or False for the following statements.
1.) Coal is an inflammable fuel.
2.) The outermost part of a candle flame contains unburnt carbon particles.
3.) The heat produced, by burning completely one kilogram of a given fuel, is known as the efficiency of that fuel.
4.) All solid fuels have a higher calorific value than liquid and gaseous fuels.
5.) Sulphur dioxide gas, produced during combustion of fossil fuels, causes acid rain.
Answer: (1) False, it is flammable and on heating it catches fire. (2) False, the inner most part consists of unburnt carbon particles (3) True (4) False (5) True
C.) Tick the correct option.
1.) An example of a non-combustible substance is-
Answer: iron
2.) A fuel starts burning only when it is heated to-
Answer: its ignition temperature
3.) The highest temperature zone of a candle flame, is its-
Answer: blue zone
4.) The amount of heat produced, on complete burning of 10 kg of a given fuel, in pure oxygen, equals H kilojoule. The calorific fuel, of that fuel, would equal-
Answer: (0.1 H) kJ/kg
5.) The gas produced, due to incomplete combustion of carbon fuels, is-
Answer: carbon monoxide
3.) The highest temperature zone of a candle flame, is its-
Answer: blue zone
4.) The amount of heat produced, on complete burning of 10 kg of a given fuel, in pure oxygen, equals H kilojoule. The calorific fuel, of that fuel, would equal-
Answer: (0.1 H) kJ/kg
5.) The gas produced, due to incomplete combustion of carbon fuels, is-
Answer: carbon monoxide
D.) Answer the following questions in brief.
1.) Define the term ‘combustible material’? Give two examples of combustible materials.
Answer: Combustible materials are substances that on being heated in the presence of air easily catch fire and release heat and light energy.
Examples are coal and wood.
2.) State the three conditions that are needed for combustion to take place.
Answer: For combustion to occur they needs to be a combustible substance they also needs to be a substance that supports combustion as well as necessary heat to make the combustible substance reach ignition temperature
3.) State the condition under which ‘slow combustion of a material takes place.
Slow combustion takes place when oxygen is almost absent or is in present at all Asin the absence of oxygen leads to incomplete combustion and produces carbon monoxide as well as carbon dioxide both of which are harmful gases
4.) define calorific value of fuel
Answer – the total amount of heat energy that one KG of a fuel can produced on burning in pure oxygen or air is known as the calorific value of fuel. it is measured in kilojoules per kilogram
5.) state any two characteristics of an ideal fuel
State any two characteristics of an ideal fuel
An ideal fuel must have. High calorific value and should not produce harmful gases after burning such as carbon monoxide and sulfur residues. it would also be great if it has cheaper prices.
6.) why is water not used in controlling electrical fires
Water contains oxygen that is a combustible substance and it is required that in any kind of fire one must take precaution so that the combustible substance does not get it heated up to its ignition temperature. Also another reason being that water used to extinguish electrical fires can give electric shocks
E.) 1 draw a diagram showing the zones of candle flame labeled the zone which contains
unburned vapors of wax
unburnt carbon particles
2.) Calorific value of wood is 18,000 kJ/kg. How much of wood is required to produce 360,000 kJ of heat energy?
Answer : 20 kg of wood are needed to produce 360 000 caloric equivalents from 1 kg of wood, which provides 18 000 calorific equivalents.
3.) Why are gaseous fuels considered better than liquid or solid fuels.
Answer: Gaseous fuels can be more easily transferred from one place to another using cylinders and pipes to store and transport them
Upon combustion gaseous fuels release very less Residue that are harmful to the environment and other
Energy produced on combustion of gaseous fuels is much more than that of solid fuels
4.) Why do we say that ‘burning of fuels’ can cause ‘health hazards’?
Answer: Often incomplete combustion of fuels can release carbon monoxide gas which is said to be a toxic gas and can affect the human body
Harmful gases such as Sulphur Dioxide are you least in the combustion of coal it can cause air pollution as well as gases such as carbon dioxide in increase proportion due to these combustion can result in global warming and other serious issues