Combustion and Flame

Combustion and Flame

HOTS

1.   Give two examples of two solid fuels

2.   Classify the fuels on the basis of states.

3.   What is the principle of fire extinguishing?

4.   We can prepare tea in a paper cup and it does not catch fire. Why?

5.   Name the clean fuel recommended to use in buses.

6.   Which part of candle flame is hottest?

7.   We can boil water in a paper cup while paper catches fire easily. Explain the process.

8.   Why does charcoal not produce flame?

9.   Do all the substances catch fire on same temperature?

10.   What is the source of heat and light of the sun?

11.   What do you mean by forest fire?

12.   How does fire brigade work?

13.   What is deforestation? What is its effect?

1.   Which substance give heat and light after combustion

        a. Flame

        b. Fuel

        c. Combustion

        d. None of these

2.   Like fuel the sun also provides heat and light. The process taking place in the sun is called

        a. Combustion

        b. Nuclear process

        c. Burning

        d. All of these

3.   Coal burns with ______

        a. Flame

        b. Only glow

        c. Both flame and glow

        d. None of these

4.   Burning of charcoal in a closed room will produce

        a. Carbon dioxide

        b. Nitrogen dioxide

        c. Carbon monoxide

        d. All of these

5.   The substances which have very low ignition temperature will

        a. Catch fire easily

        b. Will not catch fire

        c. Catch fire after some time

        d. None of these

6.   CNG and LPG are the examples of

        a. Solid fuels

        b. Liquid fuels

        c. Gaseous fuels

        d. They are not fuels

7.   Ignition temperature is

        a. Lowest temperature at catch fire

        b. Higher temperature at catch fire

        c. Any temperature

        d. None of these

8.   Combustion is a

        a. Chemical process

        b. Physical process

        c. Both of these processes

        d. None of these processes

9.   The products of combustion are

        a. Carbon dioxide and water

        b. Oxygen and water

        c. Only carbon dioxide

        d. Only oxygen

10.   There are following zones of a flame

        a. Two

        b. Three

        c. Four

        d. No any zone

ANSWERS

1.    B

2.    B

3.    B

4.    C

5.    A

6.    C

7.    A

8.    A

9.    A

10. B

1.  What is the difference between burning of a candle and burning of coal?

2.  Classify fuels?

3.  Write name of some incombustible substances

4.  What do you mean by an ignition temperature?

5.  What are the requirements to produce fire?

6.  How many types of combustion are there?

7.  Give examples of the substances which give flame.

8.  What substances are used to extinguish fire in case of electric short circuit?

9.  Which zone of flame has highest temperature?

10.  Explain structure of flame.

11.  What are the characteristics of good fuel?

12.  What are the ill effects due to the increasing consumption of fuel?

13.  Draw a diagram to explain that air is essential for combustion.

14.  What are the products of any fuel?

QUESTIONS FROM TEXTBOOK

Q.1.  List conditions under which combustion can take place. Ans. Conditions necessary for combustion are:

           (i) Presence of a combustible substance.

           (ii) Attainment of ignition temperature.

           (iii) Proper supply of air to provide oxygen.

Q.2.  Fill in the blanks.

           (a) Burning of wood and coal causes _________ of air.

           (b) A liquid fuel used in homes is _________.

           (c) Fuel must be heated to its_________before it starts burning.

           (d) Fire produced by oil cannot be controlled by_________.

Ans. (a) pollution                                    (b) kerosene.

           (c) ignition temperature           (d) water.

Q.3.  Explain how the use of CNG in automobiles has reduced pollution in our cities. The use of CNG in place of petrol and diesel reduce pollutions in following ways:

           (i) It produces less carbon monoxide gas.

           (ii) It produces less carbon dioxide gas.

           (iii) It produces less amount of sulphur dioxide and nitrogen dioxide which cause acid rain.

           (iv) No residue remains after combustion.

Q.4.  Compare LPG and wood as fuels.

Ans. Differences:

Q.5.  Give reasons:

           (a) Water is not used to control fires involving electrical equipment.

           (b) LPG is a better domestic fuel than wood.

           (c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Ans. (a) Water is a good conductor of electricity. It conducts electricity and may result electric shock.

           (b) LPG has more calorific value and produces no pollution. So it is better domestic fuel than wood.

           (c) The ignition temperature of paper is less, so it catches fire easily. It does not catch fire when wrapped around aluminium pipe because aluminium absorbs the heat, so paper does not attain its ignition temperature.

Q.6.  Make a labelled diagram of candle flame.

Ans.

Fig. 6.2 Different zones of Candle flame

Q.7.  Name the unit in which the calorific value of a fuel is expressed.

Ans. Kilojoules per kg (kJ/kg)

Q.8.  Explain how CO2 is able to control fires.

Ans. (i) CO₂ forms a blanket around fire due to which supply of air is stopped.

           (ii) CO₂ also brings down the temperature of the fuel.

Q.9.  It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Ans. The green leaves contain some water due to which the ignition temperature of leaves increases and they do not catch fire easily while dry leaves have no water, so they catch fire easily.

Q.10.  Which zone of a flame does a goldsmith use for melting gold and silver and why?

Ans. A goldsmith uses the outer zone (non-luminous zone) of a candle flame to melt gold and silver because it is the hottest zone and has more temperature.

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. Total mass of fuel = 4.5 kg

         Total heat produced = 180,000 kJ

         Heat produced by burning 1 kg of fuel = 180,000 kJ/4.5 kg = 40,000 kJ/kg.

         So, calorific value of fuel = 40,000 kJ/kg.

Q.12.  Can the process of rusting be called combustion? Discuss.

         Ans. The process of rusting cannot be called combustion because in this process no heat and light is produced. Due to this reason iron is not considered as combustible substance.

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. The water heated by Ramesh will get heated in a shorter time because he kept his beaker near the hottest zone of the flame.