COMBUSTION AND FLAME
1. Combustion:A chemical process in which a substance reacts with oxygen to give off heat is called combustion.
 
2. Combustible Substance:The substance, that burns in the presence of oxygen with the evolution of heat and light is called combustible substance.
 
3. Ignition Temperature:The lowest temperature at which a substance catches fire is called its ignition temperature.
 
4. Inflammable Substance:The substance, which have very low ignition temperature and can easily catch fire with a flame are called Inflammable substances.
 
5. Rapid Combustion:A combustion, that takes place rapidly/high speed, with the production of heat and light is called rapid combustion.
 
6. Spontaneous Combustion:A combustion in which a material suddenly bursts into flames, without the application of any apparent cause called spontaneous combustion.
 
7. Explosion:The process of combustible in which a large amount of gases are evolved with the production of tremendous amount of heat, light and sound, is called explosion.
 
8. Flame:When the combustible substance and the supporter of combustion are in gaseous form, it is called flame.
 
9. Luminous Zone of Flame:The middle zone of partial combustion that is yellow in color and produces light, is called luminous zone of flame.
 
10. Non-luminous Zone of Flame:It is the outer zone of flame, that is faintly blue in color and undergo complete combustion of the substance.
 
11. Fuels:A fuel is a substance, which may be burnt to produce considerable heat without the formation of undesirable products.
 
12. Ideal Fuel:The fuel, which fulfills all the requirement for a particular use is called as ideal fuel.
 
13. Calorific Value:The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. It is expressed in a unit called as kilojoule per kg (kJ/kg).
14. Deforestation:It is the process of cutting of trees, to use the wood as a fuel, is called deforestation.
 
 
15. Global Warming:It is the rise in to temperature of the atmosphere of the earth due to the combustion of fuels.
 
16. Acid Rain:When the pollutant like sulphur dioxide and nitrogen oxides dissolve in rainwater, it forms an acid. The rain of that acid is called acid rain.
 

 
Q.1. List conditions under which combustion can take place.

Ans.There are three essential conditions of combustion:
  1. Presence of a combustible substance.
  2. Presence of oxygen, i.e., supporter of combustion.
  3. Attainment of ignition temperature.
 
Q. 2. Fill in the blanks:
  1. Burning of wood and coal causes ……………. of air.
  2. A liquid fuel, used in homes is ……………. .
  3. Fuel must be heated to its …………   …………... before it starts burning.
  4. Fire produced by oil cannot be controlled by ……………  .
Ans.  a) pollution
          b)  LPG
          c) ignition temperature
          d) water.
 
Q.3. Explain how the use of CNG in automobiles has reduced pollution in our cities.

Ans.
CNG is cheap, readily available and highly combustible. It has high calorific value. It does not produce gases or leaves residues when used in automobiles, so it reduced the pollution in our cities.
The use of CNG in automobiles has reduced pollution in our cities because CNG produces the harmful product in very small amount and it is a cleaner fuel.
 
Q.4. Compare LPG and wood as fuels.

Ans.

LPG                                 Wood
  1. No residue after burning.
  2. Can be transport through pipe lines, and cylinder.
  3. Burn easily.
  4. Low ignition temperature.
  5. No smoke on burning.
  • Leave a lot of ash on burning.
  • Cannot be transport easily like LPG.
  •  
  • Catch fire with more difficulty.
  • High ignition temperature.
  • Burn with smoke.
  •  
 
Q.5. Give reasons:
  1. Water is not used to control fires involving electrical equipment.
  2. LPG is a better domestic fuel than wood.
  3. Paper by itself catches fire easily whereas a piece of paper wrapped around aluminium pipe does not.
Ans.

(a) Water is not used to control the fire involving electric equipment because it is a good conductor of electricity.
         (b) LPG is better domestic fuel than wood because it neither produce gases nor leaves residues that pollute the environment.
         (c) The paper by itself catches fire easily because its ignition temperature is low, while a piece of paper wrapped around an aluminium pipe does not catches fire because its ignition temperature rises.
 
Q.6. Make a labeled diagram of a candle flame.

Ans.

 
 

 
 
 
                    Fig.6.1.Different zones of a candle flame
 
Q.7. Name the unit in which the calorific value of a fuel is expressed.
Ans.The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg).
 
Q.8. Explain how CO2is able to control fires. .
Ans.CO2, being heavier than oxygen, covers the fire like blanket and also brings down the temperature of fuel. Since the contact between the fuel and oxygen is cut off, and the fire comes under control.
 
Q.9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Ans.To burn a heap of green leaves is difficult, because its ignition temperature is high, but dry leaves catch fire easily as its ignition temperature is very low.
 
Q.10. Which zone of a flame does a goldsmith use for melting gold and silver and why?
Ans.A goldsmith uses the outermost zone of a flame for melting gold and silver because it is the hottest zone of the flame (temperature = 800°C) and is non-luminous in nature.
 
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.The calorific value of the fuel:
                                                                            heat produced                1,80,000 kJ
         Calorific value      =                         -------------------------------        -----------------------              = 40,000 kJ/kg.
                                                                               amount of fuel               4.5 kg
 
Q.12. Can the process of rusting be called combustion? Discuss.
Ans.The process of rusting cannot be called as combustion because neither release of energy nor heat and light are produced during it, while in combustion- release of energy takes place with heat and light.
 
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.Ramesh's water will get heated in a shorter time.
 
ADDITIONAL IMPORTANT QUESTIONS

Q.1. In which form (solid, liquid, gas) carbon dioxide be stored in cylinders?
Ans.Carbon dioxide can be stored as a liquid in cylinders.
 
Q.2. What is rapid combustion?
Ans.A combustion that takes place at a high speed-is known as rapid combustion.
 
Q.3. What chemicals are used in the preparation of matchsticks?
Ans.The head of safety match contains only antimony trisulphide and potassium chlorate.
           
Q.4. Which have higher ignition temperature - kerosene oil or wood?
Ans.The kerosene oil has lower ignition temperature than wood.
 
Q.5. Why water is not suitable as fire extinguisher for fires involving oil and petrol?
Ans.As we know, water is heavier than oil so it sinks below the oil and oil keep burning on the top.
Q.6. Define combustible substances.
Ans.The substance that can react with oxygen and give out heat and light i.e., undergo combustion, is called combustible substances.
 
Q.7. Why we wrapped a blanket around a person who caught fire?
Ans.We wrapped a blanket around a person who caught fire, because the fire stops getting the oxygen whatever is required amount for the combustion and it extinguishes.
 
Q.8. What do you mean by inflammable substances?
Ans. The substance which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances. For examples: spirit, alcohol, etc.
 
 
Q.9.Charcoal does not burn with flame but glows only
Ans.Charcoal does not burn with flame because it is non-volatile in nature or does not vapourise on .burning, so it glows only.
 
Q.10. What is meant by the term ‘fuel’?
Ans.A fuel is a substance, which may be burnt to produce considerable heat without the formation of undersirable products.
 
Q.11. Why water is not used to control the fire by electric short circuit?
Ans. Water is not used at all to control the fire by electric short circuit because it is a good conductor of electricity and may result in electrocution or electric shock.
 
Q.12. Why any of the fuel is not considered as an ideal fuel?
Ans.All the fuel is not considered as an ideal fuel because they are differ in their cost and efficiency, i.e., its calorific value.
 
Q.13. “Food is a fuel for our body”. Explain how?
Ans.In our body, food is broken down by reaction with oxygen and heat is produced that is why food is a type of fuel for our body.
 
Q.14. Why we are advised never to sleep in a room with burning coal fire in it?
Ans.In the presence of less amount of oxygen the carbon monooxide gas produced by incomplete combustion of coal. It is a poisonous gas and can kill the person sleeping in a closed room.
 
Q.15. Explain the term “global warming”.
Ans.The combustion of fuels release carbon dioxide in the environment. When the percentage of carbon dioxide increases in the atmosphere and makes the earth surface hot-it is believed to cause global warming.
 
Q.16. What is acid rain?
Ans.The gases like nitrogen oxide, sulphur dioxide etc. present in the atmosphere as pollutants. When these gases dissolve in rain water, it forms acids and when it reaches to the earth as rain, called as acid rain.
 
Q.17. What are the three essential requirements for producing fire?
Ans.The three essential requirements are
  1. Fuel
  2. Air (to supply oxygen)
  3. Heat (to raise the temperature of the fuel beyond the ignition temperature).
 
Q. 18. Why CNG is preferable for vehicles in respect to petrol and diesel?
Ans. CNG (compressed natural gas) is preferable for vehicles in respect to petrol and diesel, because:
  1. It leaves least residues
  2. It is cheaper.
  3. It is eco-friendly.
 
Q.19.What is spontaneous burning?
Ans.In a heap of several substances, when they catches fire, they undergo slow oxidation with evolution of heat. At certain stage when the temperature becomes more than the ignition temperature of any one of the constituent-all of a sudden, it starts burning. This is called spontaneous burning.
 
Q.20. Give the characteristics of ideal fuel.
Ans.1. It is readily available.
        2. It is cheap.
        3. It burns easily at moderate rate.
        4. It produces a large amount of heat.
        5. It does not leave behind any undesirable substances.
 
Q.21. What are the constituents of a foam type fire extinguisher?
Ans.The foam type fire extinguisher is also called as `Soda acid' fire extinguisher. The constituents are:
         (a) Dilute sulphuric acid
         (b) Sodium bicarbonate (soda).
 
 
 
 
 
 

Fig.6.3.Foam type fire extinguisher
 
       When it is operated, it comes out under pressure in the form of a foam, which covers the surface of fire and controls it.
 
Q.22. What are the different harmful products formed by the burning of a fuel?
Ans.The harmful product formed by the burning of a fuel:
  1. Carbon fuels release unburnt carbon particles, which are dangerous pollutants that causes respiratory disorders.
  2. Incomplete combustion of carbon fuels gives carbon monooxide a poisonous gas that can even kill a person sleeping in a closed room.
 
 
Q.23. Describe the various zones of a flame.
Ans.A flame has four zones in it:
  1. The outermost thin transparent faint bluish nonuminous region of complete combustion. It is the hottest zone of the flame.
  2. The middle bright luminous zone of partial combustion. It is the moderately hot zone.
  3. The innermost, coldest dark zone, consists of hot vapour and called as zone of no combustion.
  4. Blue zone near the bottom of the flame is due to burning of carbon monoxide. CO is formed due to incomplete combustion.
 
 
 
 
 
 
 

Fig.6.4.Different zones of a candle flame
 
 
Q.24. With the help of given table, mark the combustible and non-combustible substances of your daily life.

Material Combustible/Non combustible
Wood


Paper


Iron nails
Kerosene oil
Stone piece
Straw
Charcoal


Match sticks


Glass
 
 
Ans.
 
Material Combustible/Non combustible
Wood

Combustible
Paper

Combustible
Iron nailsNon-combustible
Kerosene oilCombustible
Stone pieceNon-combustible
StrawCombustible
Charcoal

Combustible
Match sticks

Combustible
GlassNon-combustible
 
 
 
Q.25. With the help of an experiment, show that oxygen (air) is necessary for the burning of a candle.
Ans.To show the experiment we have to fix three lighted candle on a table, and put a glass chimney over it.



        (a)                                            (b)                                      (c)   
 
Fig.6.2.Showing that air is essential for burning
 
The chimney (Fig. a) rested on wooden blocks in such a way that air can enter the chimney-the candle will continue burning, because air can enter the chimney from below.
The chimney (Fig. b) rested on the table with no way for air-the flame flickers and produces smoke.
The chimney (Fig. c) rested on table and covered from top with glass plate-the flame goes off because the air is not available.
 
                                                

                                                   OBJECTIVE TYPE QUESTION

Q.1. Fill in the blanks with appropriate words:
  1. ..................  forms poisonous carbon monoxide gas.
  2. …………..  is expressed in terms of its calorific value.
  3. .................  have very low ignition temperature.
  4. ………….. is essential for combustion.
  5. The substance, which burn in air are called …………..  .
  6. .................  is better domestic fuel than wood.
  7. Goldsmith uses the …………. zone of the flame for melting gold and silver.
 
Q. 2. Match the following items given in Column ‘A’ with that in Column ‘B’.


Column AColumn B
  1. Fire extinguisher
  2. Slow oxidation
  3. Kindling temperature
  4. Tidal energy
  5. Fossil fuel
  6. Oxygen gas
  7. LPG
  8. Alcohol
  1. Burning of candle
  2. Renewable source
  3. Natural gas
  4. Cooking gas
  5. Inflammable
  6. Burns
  7. Carbon dioxide
  8. Supporter of combustion
 
 
Q.3. State whether the statement given below are True or False.
  1. Food is a fuel for our body.
  2. Burning of charcoal produces flame with four distinct zones.
  3. The fuel can be only liquid in nature.
  4. Sun produces heat and light because of combustion.
  5. It is easy to burn a piece of wood through matchstick.
  6. Soda acid fire extinguisher contains sodium bicarbonate + dil. Sulphuric acid.
  7. The inner central-dark zone of a candle flame is the hottest region.
  8. The principle of all fire-extinguisher is to cut off the air supply and to cool the burning substance to below its ignition temperature.
 
Q. 4. Choose the correct option in the following questions:
  1. Which one of the following gas is used in combustion?
a) Hydrogen                                           b) Oxygen
c) Nitrogen                                             d) Carbon dioxide
 
  1. The burning of LPG is an example of
a) rapid combustion                               b) spontaneous combustion
c) slow combustion                                d) explosion
  1. A temperature at which the substance burns is called
a) melting                                               b) boiling temperature
c) kindling temperature                          d) evaporation
 
  1. Which is non-renewable source of energy?
a) Natural gas                                         b) Wind energy
c) Tidal energy                                       d) Mechanical energy
 
  1. Which of the following is not a fossil fuel?
a) Coal                                                    b) Petroleum
c) Natural gas                                         d) Water gas
 
  1. Which gas helps in the process of combustion?
a) Cooking gas                                       b) Nitrogen gas
c) Oxygen gas                                        d) Producer gas
 
  1. The amount of heat energy produced on complete combustion of 1 kg of a fuel is called
a) calorific value                                    b) significant value
c) heat value                                          d)  internal energy
 
  1. Which zone represents the partial combustion in candle flame?
a) Outer zone                                         b) Middle zone
c) Inner zone                                         d) Lower zone
 
  1. Burning coal in a closed room will produce
a) nitrogen oxides                                  b) carbon dioxide.
c) carbon monoxide                               d) oxygen
 
  1. Substances which catch fire are called
a) acids                                                  b) bases
c) combustible                                      d)  burners
 
  1. Out of these, which is able to control fires?
a) NH3                                                  b) H2
c) CO2                                                  d) F2
 
  1. Which zone of a flame does a goldsmith use for melting gold and silver?.
a) Outer zone                                        b) Middle zone
c) Inner zone                                        d) Lower zone
 
  1. Calorific value of a fuel is expressed in
a) kilojoule per kilogram                     b) kilojoule per gram
c) joule per milligram                          d) kilojoule per milligram
 
  1. Which is non-combustible substance?
a) Wood                                               b) Paper
c) Iron nails                                         d) Straw
 
  1. Acid rain contains mainly
a) oxygen and nitrogen gas                 b) fluorine and chlorine gas
c) magnesium oxide                           d) nitrogen oxide and sulphur dioxide
 
 
ANSWERS TO OBJECTIVE TYPE QUESTIONS
 
Q.1. Fill in the blanks:
  1. Incomplete combustion             ii. Fuel efficiency       iii. Inflammable substances
  2. Oxygen (in air)                          v. combustible            vi. LPG
  3. outermost.
 
Q.2. Match the items under Column ‘A’ and Column ‘B’:
Column ‘A’Column ‘B’
  1. Fire extinguisher
  2. Slow oxidation
  3. Kindling temperature
  4. Tidal energy
  5. Fossil fuel
  6. Oxygen gas
  7. LPG
  8. Alcohol
  1. Carbon dioxide
  2. Burning of candle
  3. Burns
  4. Renewable source
  5. Natural gas
  6. Supporter of combustion
  7. Cooking gas
  8. Inflammable
 
Q. 3. True/False:
     i) True                 ii) False                iii) False                  iv) False            
    v) False               vi) True                vii) False                 viii) True.             
 
Q.4. Choose the correct option:
      (i) (b)                   (ii) (a)                  (iii) (c)                (iv) (a)                   (v) (d)
     
    (vi) (c)                 (vii) (a)                 (viii) (b)               (ix) (c)                   (x) (c)
 
    (xi) (c)                 (xii) (a)                 (xiii) (a)              (xiv) (c)                 (xv) (d).