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Page No 85:

Question 1:

What is combustion?

Answer:

Combustion is a process of burning a substance in the presence of air or oxygen, as a result of which heat and light are produced.

Page No 85:

Question 2:

Differentiate between combustible and non-combustible substances. Give two examples of each.

Answer:

 

 Combustible substances  Non combustible substances
 Combustible substances are those which readily burn in the presence of air or oxygen to produce heat and light. Non-combustible substances are those which do not readily burn in the presence of air or oxygen to produce heat and light.
 Examples include wood and paper.  Examples include glass and sand.

Page No 85:

Question 3:

Differentiate between complete combustion and incomplete combustion.

Answer:

Complete combustion  Incomplete combustion
 Complete combustion is a combustion process that takes place in the presence of adequate air or oxygen. Complete combustion is a combustion process that takes place in the presence of inadequate air or oxygen.
Complete combustion results in the formation of carbon dioxide, water, heat and light. Incomplete combustion results in the formation of carbon monoxide, soot, water, heat and light.

Page No 85:

Question 4:

State the three necessary conditions for combustion.

Answer:

The process of combustion can take place only when:

(i) A combustible substance (fuel) is present.
(ii) A substance (air) which supports the process of combustion should be present .
(iii) The combustible substance attain the ignition temperature (minimum required heat).

Page No 85:

Question 5:

What is ignition temperature? Why are substances like alcohol and petrol called inflammable substances?

Answer:

All substances can burn only when it attains a certain minimum temperature. This particular temperature at which the substances burn in the presence of air or oxygen is called as ignition temperature. Substances such as alcohol and petrol have a low ignition temperatures, and easily catch fire. Therefore, they are called inflammable substances.

Page No 85:

Question 6:

Describe the two common type of fire extinguishers.

Answer:

The most used fire extinguishers are,
(i) Carbon dioxide fire extinguishers: In this type of fire extinguishers, carbon dioxide which is a non supporter of combustion, is filled in cylinders under high pressures. When released, it cuts off the air supply to the burning substance and extinguishes fire.
(ii) Soda acid fire extinguishers:  In this type of fire extinguishers, concentrated solution of sodium hydrogen carbonate and sulphuric acid are stored separately in two chambers. On using the fire extinguisher, both the substances come in contact with each other producing carbon dioxide.

Page No 85:

Question 1:

Write one word for the following.

1. The process of burning a substance in the presence of air or oxygen ....................
2. A region where combustion of fuel takes place ....................
3. Substances that produce heat and light energy on burning ....................
4. A fuel that is generally black or brownish-black in colour ....................
5. A type of coal with carbon content of around 92−98% ....................

Answer:

1. Combustion
2. Flame
3. Combustible substances
4. Coal
5. Anthracite

Page No 85:

Question 1:

Which of the following takes place in inadequate amount of air or oxygen?
(a) Complete combustion
(b) Incomplete combustion
(c) Explosion
(d) Both (a) and (b)

Answer:

(a) Incomplete combustion.
Incomplete combustion takes place in inadequate amount of air or oxygen.

Page No 85:

Question 2:

Which of these is necessary for combustion?
(a) Combustible substance
(b) Attainment of ignition temperature
(c) Supporter of combustion
(d) All of these

Answer:

(d) All of these
Combustible substance, supporter of combustion and attainment of ignition temperature are necessary for the process of combustion.

Page No 85:

Question 3:

A non-luminous flame appears
(a) red
(b) blue
(c) white
(d) pink

Answer:

(b) blue
A non-luminous flame appears blue.

Page No 85:

Question 4:

Which of these has the highest carton content?
(a) Anthracite
(b) Bituminous coal
(c) Lignite
(d) Natural gas

Answer:

(a) Anthracite
Anthracite coal has the highest carbon content.

Page No 85:

Question 5:

CNG stands for
(a) compressed natural gas
(b) compact natural gas
(c) carbonated natural gas
(d) combustible neutral gas

Answer:

(a) Compressed Natural Gas

CNG stands for Compressed Natural Gas.

Page No 85:

Question 1:

Match the following.

Column A Column B
Explosion Coke
The outer zone of a flame Sudden release of heat
Fossil fuels CNG
Non-polluting fuel Exhaustible
Hard and dry fuel Blue in colour

Answer:

Column A Column B
Explosion Sudden release of heat
The outer zone of a flame Blue in colour
Fossil fuels Exhaustible
Non-polluting fuel CNG
Hard and dry fuel Coke



Page No 86:

Question 7:

Differentiate between luminous and non-luminous flame.

Answer:

 

 Luminous flame  Non-luminous flame
This type of flame is observed when there is no sufficient oxygen. This type of flame is observed when there is sufficient oxygen.
Luminous flame will be yellow in colour and emits a lot of light. Non-luminous flame will be blue in colour and emits very little light.
Black soot and other residues are left behind. No residue is left behind.

Page No 86:

Question 8:

What is a fuel? Give two examples each of solid, liquid, and gaseous fuels.

Answer:

A fuel is a substance which produces heat and light on burning. Depending upon the state of existence at room temperature, fuels can be mainly classified into three types:
(i) Solid fuels : Examples include wood and coal.
(ii) Liquid fuels : Examples include kerosene and petrol.
(iii) Gaseous fuels : Examples include petroleum gas and natural gas.

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Question 9:

Why are methane and LPG considered ideal for use as domestic fuels?

Answer:

Methane and LPG are considered to be ideal fuels for domestic use as they contain high calorific values. Apart from this they do not emit any smoke during burning and therefore, do not cause any pollution.

Page No 86:

Question 10:

Write any two ways in which we can conserve fossil fuels.

Answer:

Fossil fuels are exhaustible resources which takes millions of years in the formation. It is very necessary to conserve these resources which can be done in following ways:
(i) The existing resources should be used economically and any wastage or unnecessary use should be avoided.
(ii) To meet the growing needs, the use of alternate sources of energy like wind energy, solar energy, etc., should be appreciated.

Page No 86:

Question 11:

Differentiate between exhaustible and inexhaustible natural resources. Give two examples of each.

Answer:

 Exhaustible resources  Inexhaustible resources
These are the natural resources whose reserves end up after continuous usage over a period of time. These are the natural resources which does not end, even after continuous usage over a period of time.
Fossil fuels and forests are some examples for exhaustible resources. Sunlight and wind are some examples for inexhaustible resources.

Page No 86:

Question 1:

Explain the different zones of a candle flame.

Answer:

Depending upon the oxygen available, a candle flame exhibits three zones:

(i) Outer zone: In this zone, the candle vapours burn in the presence of adequate oxygen. This part of the flame will be blue in colour which emits less light and high heat.
(ii) Middle zone: In this zone, the candle vapours burn in the presence of inadequate oxygen producing carbon monoxide. This part of the flame will be yellow in colour which emits more light and less heat.
(iii) Inner zone: In this zone, the candle vapours remain unburnt due to the absence of oxygen. This part of the flame will be black in colour which does not emit any heat or light.

Page No 86:

Question 2:

What is a calorific value of a fuel? Write any four characteristics of an ideal fuel.

Answer:

The amount of heat produced when one gram of fuel is burnt is called the calorific value of the fuel. The unit used to measure the calorific value of a fuel is kilojoules. A fuel is said to be an ideal fuel if it fulfils the following characteristics:
(i) It should be cheap in cost and easily available.
(ii) It should have a high calorific value.
(iii) The fuel should be easy to transport and safe to handle and store.
(iv) It should produce a smokeless fire on burning and should not cause pollution.

Page No 86:

Question 3:

What are fossil fuels? How were coal and petroleum formed?

Answer:

As the name indicates, the fossil fuels are the fuel resources which are formed due to the buried remains of plants and animals over a period of million years. Examples of fossil fuels include coal and petroleum.
Coal was formed when trees and plants that grew in humid, swampy areas died and got buried in swampy soil, which were later covered by layers of the sediments for about 300-400 million years.
Petroleum was also formed in a similar manner due to the burial of marine organisms which died millions of years ago.

Page No 86:

Question 4:

What are the products obtained on refining petroleum? Write their main uses.

Answer:

The refining of petroleum is done through a process called fractional distillation. The byproducts that are obtained during refining of petroleum are also used for various purposes like,
(i) Petroleum gas: The liquified form of this gas, called LPG is used for domestic purposes.
(ii) Petrol: This is one of the main sources of fuel to run automobiles. It is also used in dry cleaning and in some chemicals.
(iii) Kerosene: Used for domestic purposes such as to light the lamps and stoves. Also used as a jet fuel.
(iv) Diesel: This is one of the main sources of fuel to run heavy automobiles and generators.
(v) Fuel oil: Fuel oil is used in power stations and ships.
(vi) Lubricating oil: Used in the manufacture of lubricants, paraffin wax and asphalt.

Page No 86:

Question 5:

Name any four air pollutants and describe their harmful effects.

Answer:

The combustion of fossil fuels produces smoke and particulate matter that cause air pollution. These pollutants adversely affect the life of organisms. The pollutants that cause air pollution are:

(i) Carbon monoxide: This gas is produced when the fossil fuels undergo incomplete combustion. Carbon monoxide causes headache and dizziness that may even lead to coma and death.
(ii) Carbon dioxide: The increase in the levels of carbon dioxide leads to an increase in the global temperature causing the melting of polar ice caps and glaciers; thereby, resulting in an increase in the sea levels and submergence of coastal areas.
(iii) Sulphur dioxide and Nitrogen oxides: These gases react with the water vapour present in the atmosphere to form acids. These acids come down with the rain as acid rain. Acid rain is very harmful to living beings and buildings on the surface of the earth.
(iv) Soot particles: These are produced when fossil fuels undergo incomplete combustion. The soot particles present in the air enter the human body during breathing and cause respiratory ailments.



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