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CBSE Sample Paper Class 8 Science Combustion and Flame
Combustion and Flame
1.) Answer the short questions (12×1)
a.) What is combustion?
b.) What is fuel?
c.) By which reaction heat and light is produced in the Sun?
d.) What is ignition temperature?
e.) How Egyptians made matchstick?
f.) What are the chemical components of head of a safety matchstick?
g.) What is inflammable substances?
h.) What are the essential requirements for producing fire?
i.) What is used for extinguishing fire involving electrical and inflammable materials?
j.) What is explosion?
k.) What is calorific value?
l.) What is acid rain?
2.) Briefly answer the following questions (5×3)
a.) Write the mechanism of lighting a matchstick.
b.) Why fire is used to extinguish fire?
c.) Why CO2 is best extinguisher of fires involving electrical and inflammable materials?
d.) Classify combustion and describe them.
e.) How burning fuel is harmful for us?
3.) Fill in the blanks (10×1)
a.) Food is ______ to our body.
b.) In the Sun, heat and light are produced by _______ reactions.
c.) Head of match stick contains ______ and ________.
d.) Substances which easily catch fire are called _______.
e.) Most common fire extinguisher is _________.
f.) Requirements of producing fire is _______, _______ and ________.
g.) Non-luminous zone of the flame has _______ temperature.
h.) The unit for calorific value of a fuel is ________.
i.) In automobiles use of petrol and diesel is replaced by _______.
j.) Fuel efficiency is expressed in _________.
4.) Write true or false (6×1)
a.) Oxygen is not essential for fire.
b.) Water is a common fire extinguisher.
c.) There are three zones of a flame.
d.) Carbon dioxide is an essential for extinguishing fire involving electrical material.
e.) Acid rain us good for environment.
f.) Carbon monoxide is a healthy gas.
(5) Match the columns (7×1)
Material |
Combustible | Non-combustible |
Paper |
|
|
Iron rods |
||
Glass |
|
|
Wood |
||
Petrol |
|
|
Steel plate |
||
Matchstick |
|
Answer
(1) Answer the short questions (12×1)
(a) What is combustion?
Answer – Combustion is a process in which substances reacts with oxygen to give off heat.
(b) What is fuel?
Answer – The substance which undergoes the process of combustion is called fuel.
(c) By which reaction heat and light is produced in the Sun?
Answer – Heat and light is produced in the Sun by nuclear reaction.
(d) What is ignition temperature?
Answer – Ignition temperature is the lowest temperature at which substance catches fire.
(e) How Egyptians made matchstick?
Answer – Egyptians made matchstick by using small pieces of pinewood, which was dipped into sulphur.
(f) What are the chemical components of head of a safety matchstick?
Answer – The components of head of safety matchstick is antimony trisulphide andpotassium chlorate.
(g) What is inflammable substances?
Answer – The substances characterized by very low ignition temperature and which catch fire easily are called inflammable substances.
(h) What are the essential requirements for producing fire?
Answer – Fire gas three essential requirements, without even one of them we can’t produce fire. These essential requirements are fuel, air and heat.
(i) What is used for extinguishing fire involving electrical and inflammable materials?
Answer – Carbon dioxide gas is used for extinguishing fire involving electrical and inflammable materials.
(j) What is explosion?
Answer – A reaction, which is characterized by sudden evolution of heat, light and sound, and produces large amount of gas, is called explosion.
(k) What is calorific value?
Answer – Calorifc value is used to measure the energy produced by heat.
Calorific value is the energy produced by the complete combustion of 1kg of fuel.
(l) What is acid rain?
Answer – Oxides of sulphur and nitrogen produced by the burning of fuel dissolves in rain water and form acids. This is called acid rain.
(2) Briefly answer the following questions (5×3)
(a) Write the mechanism of lighting a matchstick.
Answer – Matchstick head consists of antimony trisulphide and potassium chlorate. The rubbing surface of the box contains powered glass and little red phosphorus. When the matchstick head is rubbed against it, the red phosphorus converts to white phosphorus and reacts with potassium chlorate. This reaction produces enough heat to ignite the antimony trisulphide and start burning.
(b) Why fire is used to extinguish fire?
Answer – Fire is the most common fire extinguisher. It extinguishes fire by following mechanisms,
- Water cools the combustible material which decreases it’s ignition temperature.
- Decreasing ignition temperature prevents the fire from spreading.
- The water vapour produced by the heat surrounds the material and cuts of air supply.
(c) Why CO2 is best extinguisher of fires involving electrical and inflammable materials?
Answer – Water isn’t used for extinguish fires involving electrical and inflammable materials. In the place of water, carbon dioxide is used. This is because,
- Carbon dioxide is heavier than oxygen, so it covers the fire like blanket.
- The covering cuts off the air supply of fire. So the fire is controlled.
- Carbon dioxide also doesn’t harm the electrical materials.
(d) Classify combustion and describe them.
Answer – Combustion is two types, rapid combustion and spontaneous combustion.
- Rapid combustion –In this type of combustion the gas burns rapidly, producing light and heat.
- Spontaneous combustion – In this type of combustion, the combustible material is suddenly burst into flames.
(e) How burning fuel is harmful for us?
Answer – Burning of fuel is harmful for use because,
- Burning of wood, coal etc. releases unburnt carbon which can cause pollution and diseases such as asthma.
- Incomplete combustion releases carbon monoxide gas, which is a very poisonous gas.
- Combustion of fuel increases the carbon dioxide in the air, which can cause global warming.
- Burning of fuel produces oxides of sulphur and nitrogen, which causes acid rain.
(3) Fill in the blanks (10×1)
(a) Food is fuel to our body.
(b) In the Sun, heat and light are produced by nuclear reactions.
(c) Head of matchstick contains antimony trisulphide and potassium chlorate.
(d) Substances which easily catch fire are called inflammable substance.
(e) Most common fire extinguisher is water .
(f) Requirements of producing fire is fuel ,air and heat.
(g) Non-luminous zone of the flame has high temperature.
(h) The unit for calorific value of a fuel is kilojoule per kilo .
(i) In automobiles use of petrol and diesel is replaced by CNG .
(j) Fuel efficiency is expressed in calorific value .
(4) Write true or false (6×1)
(a) Oxygen is not essential for fire.
Answer – False.
(b) Water is a common fire extinguisher.
Answer – True.
(c) There are three zones of a flame.
Answer – True.
(d) Carbon dioxide is an essential for extinguishing fire involving electrical material.
Answer – True.
(e) Acid rain us good for environment.
Answer – False.
(f) Carbon monoxide is a healthy gas.
Answer – False.
(5) Match the columns (7×1)
Material |
Combustible | Non-combustible |
Paper | ✔ |
|
Iron rods |
✔ | |
Glass |
✔ |
|
Wood |
✔ | |
Petrol | ✔ |
|
Steel plate |
✔ | |
Matchstick | ✔ |
|