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Saturday, August 11, 2012

Class 8th solved Question Combustion and Flame by Jsunil Tutorial

Class 8th solved question Combustion and Flame
1. Define Fuel. Give examples of solid, liquid and gaseous fuels.
Ans: The substance that undergoes combustion is called fuel. Fuels are substances which, on combustion produce heat energy without producing undesirable by-products.
Fuels are of three main types. They are :-
i) Solid fuels :- Eg:- wood, coal, charcoal etc.
ii) Liquid fuels :- Eg:- kerosene, petrol, diesel etc.
iii) Gaseous fuels :- Eg:- CNG, LPG, biogas, hydrogen etc.
2. Differentiate between combustible and non-combustible substances with two examples of each kind?
Ans: Combustible substances:- Substances which burn in air to produce heat and light are called combustible substances.  Eg :- wood, coal, charcoal, kerosene, petrol, diesel, liquified petroleum gas (LPG), compressed natural gas (CNG) etc.
Substances like stone, glass, iron nails, etc. do not burn on being exposed to flame. Such substances are called non-combustible substances.
3. What is combustion?
Ans:  Combustion: - The chemical process in which a substance reacts with oxygen to produce heat is called combustion.  Combustion is the burning of substances in air or oxygen to release heat and light.
e.g. magnesium burns to form magnesium oxide and produces heat and light.
4. Why does a candle stop burning when covered with a glass tumbler?
Ans: A candle stop burning when covered with a glass tumbler due to absence of oxygen that support burning. Air is necessary for combustion.
5. How is spontaneous combustion different from explosion?
Ans: Spontaneous combustion:- is combustion in which a substance burns spontaneously and produces heat and light without the help of external heat. Eg:- phosphorus burns spontaneously at room temperature
Explosion:- is a combustion in which a substance burns suddenly and produces heat, light and sound with the help of heat or pressure. Eg:- explosion of crackers on applying heat or pressure.
6. Special care should be taken to store kerosene oil. Give reason.
Ans: kerosene oil is combustible substance and produce heat and light immediately so Special care should be taken to store kerosene oil.
7. When the clothes of a person catch fire, the person is covered with a blanket to extinguish the fire. Can you guess why?
Ans: Blanket cut off supply of air or oxygen to extinguish the fire
8. Why is L.P.G labeled as inflammable substance?
Ans:  L.P.G has low ignition temperature and catches fire easily so L.P.G labeled as inflammable substance.
9. Which substance added to LPG to detect any leakage?
Ans: A small amount of ethyl mercaptan, an inert gas with a characteristic odour, is added to LPG to detect any leak.
10. How does water help to extinguish fire?
Ans:  When water is poured over a burning substance, it absorbs heat from the substance. As a result the temperature of the substance falls below the ignition temperature, and it stops burning

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