COMBUSTION AND FLAME

The calorific values of petrol and CNG are 45000 kJ/kg and
50,000 kJ/kg, respectively. If you have vehicle which can run on
petrol as well as CNG, which fuel will you prefer and why?

Forest fire produces a lot of air pollution. Write in brief about the
reasons of forest fires.

Although wood has a very high calorific value, we still discourage
its use as a fuel. Explain.

The calorific values of petrol and CNG are 45000 kJ/kg and
50,000 kJ/kg, respectively. If you have vehicle which can run on
petrol as well as CNG, which fuel will you prefer and why?

Give two examples each for a solid, liquid and gaseous fuel
alongwith some important uses.

What are the three essential requirements to produce fire? How
fire extinguisher is useful for controlling the fire.

Manu was heating oil to fry potato chips. The cooking oil all of a
sudden caught fire; he poured water to extinguish the fire. Do
you think this action was suitable. If yes, why? If not, why not?
In such a condition what should Manu have done?

You are provided with three watch glasses containing milk, petrol
and mustard oil, respectively. Suppose you bring a burning candle
near these materials one by one, which material(s) will catch fire
instantly and why?

What do you understand by fuel efficiency?

Cracker on ignition produces sound. Why?

Write True/False against the following statements and also correct
the false statement.
(a) A physical process in which a substance reacts with oxygen
to give off heat is called combustion.
(b) Water is the best extinguisher for fires involving electrical
equipment.
(c) Alcohol, CNG and LPG are inflammable substances.
(d) Increased concentration of nitrogen in air is believed to cause
global warming.
(e) Greater the calorific value, better is the fuel.
(f) Middle zone is the hottest zone of a flame.
(g) The substances which vapourise during burning, give flame.

People usually keep Angethi/burning coal in their closed rooms
during winter season. Why is it advised to keep the door open?

Fill in the blanks using the words given in the box.
ignition, petrol, combustion, calorific value,
combustible, inflammable
(a) A chemical process in which a substance reacts with oxygen
to give off heat is called __________.
(b) Wood, paper, CNG are __________ substances.
(c) The lowest temperature at which a substance catches fire is
called its __________ temperature.
(d) Ignition temperature of __________ is lower than that of wood.
(e) The substances which have very low __________ temperature
and can easily catch fire with a flame are called __________
substances.
(f) The amount of heat energy produced on complete combustion
of 1kg of a fuel is called its __________.

If you hold a piece of iron wire with a pair of tongs inside a
candle flame or a Bunsen burner flame, what will you observe?
Will it produce a flame?

Indicate whether the following statements are True or False. Also
write the false statements in their correct form.
(a) Air is necessary for combustion.
(b) Magnesium is a non-combustible metal.
(c) Carbon dioxide is an excellent fire extinguisher.
(d) Calorific value of wood is higher than that of coal.

Boojho wants to separate the following materials as combustible
and non-combustible. Can you help him?
Charcoal, chalk, stone, iron rod, copper coin, straw,
cardboard, glass, paper, candle, wood.

Why is the use of diesel and petrol as fuels in automobiles being
replaced by Compressed Natural Gas (CNG) in big cities?

Anu wants to boil water quickly in a test tube. On observing the
different zones of the flame, she is not able to decide which zone
of the flame will be best for boiling water quickly. Help her in
this activity.

Two glass jars A and B are filled with carbon dioxide and oxygen
gases, respectively. In each jar a lighted candle is placed
simultaneously. In which jar will the candle remain lighted for a
longer time and why?

Fill in the blanks in the following sentences.
(a) A ____________ process in which a 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 substances which have very ________________ ignition
temperature and can easily catch fire with a flame are called
__________ substances.

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

 Make a labelled diagram of a candle flame

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?

Can the process of rusting be called combustion? Discuss.

 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.

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

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

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

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.

Compare LPG and wood as fuels.

Explain how the use of CNG in automobiles has reduced pollution in our cities.

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 _________.

List conditions under which combustion can take place.