CLASS-8 SUBJECT SCIENCE CHAPTER-6 COMBUSTION AND FLAMES

 EVENTS CONVENT HIGH SCHOOL

01/02/2022      CLASS- 8   SESSION 2021-22
SUBJECT : SCIENCE

CHAPTER-6
COMBUSTION AND FLAMES

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Question 1.List conditions under which combustion can take place.
Answer:
Combustion can take place in the presence of:
(a) a combustible substance.
(b) oxygen, that is, the supporter of combustion.
(c) attainment of ignition temperature of the substance.

Question 2.Fill in the blanks.
(a) Burning of wood and coal causes pollutionof air.
(b) A liquid fuel, used in homes is LPG
(c) Fuel must be heated to its ignition temperature before it starts burning.
(d) Fire produced by oil cannot be controlled by water

Question 3.Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer:
The use of CNG in automobiles has reduced pollution in our cities as it is a quality fuel and has some benefits:
(a) It gives out less carbon dioxide gas, carbon monoxide gas, sulphur dioxide and nitrogen dioxide, which is beneficial as they play crucial role in global warming and acid rain.
(b) It leaves behind no residue after its combustion.

Question 4.Compare LPG and wood as fuels.
Answer:

LPG	Wood
(i) It does not cause pollution on combustion.	(i) It pollutes air on its combustion.
(ii) No smoke is produced.	(ii) It produces smoke.
(iii) It is a liquid fuel.	(iii) It is a solid fuel.
(iv) It has more calorific value (55000 kJ/kg).	(iv) It has less calorific value (17000 kJ/kg).
(v) It can be easily transported, as it is stored in cylinders.	(v) It can’t be transported easily like LPG fuels.

Very Short Answer Questions

Question 1.Name the most common fuel used in homes.
Answer:
Liquefied Petroleum Gas. (LPG)

Question 2.Name the most common fire extinguisher.
Answer:
Water

Question 3.What are the states in which a fuel may exist?
Answer:
A fuql may exist in solid, liquid or gaseous state.

Question 4.Name any two combustible substances.
Answer:
Charcoal, wood

Question 5.Does magnesium produce heat and light during its combustion?
Answer:
Yes, it does.

Short Answer Questions

Question 1.What does magnesium burn to form?
Answer:
Magnesium burns to form magnesium oxide and produces heat and light.

Question 2.What does coal produce during its combustion?
Answer:
Coal produces carbon dioxide, heat and light during its combustion.

Question 3.What is combustion?
Answer:
Combustion is a chemical process in which a substance reacts with oxygen to give off heat.

Question 4.Define ignition temperature of a fuel.
Answer:
The lowest temperature at which a fuel catches fire is called its ignition temperature.

Question 5.How does a matchstick catch fire?
Answer:
By rubbing a matchstick against a rough surface (friction), it attains its ignition temperature and thus catches fire.