Chapter- 7
COMBUSTION
1. Anu wants to boil water quickly in a test –tube. On observing the different zones of flame,
she is not able to decide which zone of flame will be best for boiling water. Help her in the
activity.
2. If you hold a piece of iron with pair of tongs inside a candle flame or Bunsen burner flame .
What will you observe? Will it produce a flame?
3. Cracker on ignition produces sound. Why?
4. What do you understand by fuel efficiency?
5. Fill in the blanks
a) A ___________ process in which substance reacts with _________ to give off heat is
called combustion.
b) When the clothes of a person catch ________, the person is covered with a
______________ to extinguish fire.
c) The _________ temperature at which a substance catches fire is called its ________
temperature.
d) The substance which have very ________ ignition temperature can easily catch fire with
flame are called _________ substances.
e) The substance which vaporize during ________, give flame.
f) The amount of heat energy produced on complete combustion of 1 kg of fuel is called its
_____________.
6. Indicate whether given statement are True or False
a) Air is necessary for combustion.
b) Magnesium is non –combustible metal.
c) Carbon dioxide is an excellent fire extinguisher.
d) Calorific value of wood is higher than that of coal.
7. Match the following
Column l Column ll
a) oxides of Sulphur and Nitrogen i) fire extinguisher
b) CNG ii) incomplete combustion of coal
c) Oxygen iii) very low ignition temperature
d) Inflammable substance iv) acid rain
e) Carbon dioxide v) necessary of combustion
f) Carbon monoxide vi) fuel of automobiles
8. Why does white phosphorus catch fire spontaneously?
9. Why a match stick can be lighted by striking its tip with any rough surface?
10. The flame of a burning candle goes off when we blow air over it strongly, why?
11. Why should not we use water to extinguish the fire caused by electric short circuit?
12. Name the gas released in the environment due to combustion of fuel leading to global
warming.
13. How does the burning of coal and diesel lead to acid rain?
14. In which part of the candle flame do you find the un-burnt wax vapour?
15. If we hold a glass slide in the luminous part of the flame, we see a circular greyish black ring
on the slide with no deposition in the centre of the ring . Explain what causes such a
formation?
16. What is an explosive combustion?
17. What do you understand by kindling temperature?
18. How is smog produced?
19. Why is use of fuel like petrol, diesel in automobiles being replaced by CNG?
20. If we bring a burning matchstick near a paper and a piece of wood .Which of them will burn
and why?
21. Give one word for following :
a) Amount of heat energy produced on completely burning one kilogram of a fuel in pure
oxygen.
b) The minimum temperature at which a given substance begins to burn.
c) A region of burning gases.
22. What happens when there is incomplete combustion of fuel?
