Class 8 Exam  >  Class 8 Notes  >  Science Class 8  >  NCERT Solutions: Combustion & Flame

NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame

Exercises

Q1. List conditions under which combustion can take place.
Ans: The conditions required for combustion to take place are:
NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame

  • Presence of a fuel.
  • Air (or oxygen).
  • Ignition temperature (minimum temperature at which a substance catches fire).


Q2. Fill in the blanks:
(a) Burning of wood and coal causes …………….of air.
Ans: Pollution

(b) A liquid fuel, used in homes is …………….
Ans: LPG

(c) Fuel must be heated to its …………  …………….before it starts burning.
Ans: Ignition temperature

(d) Fire produced by oil cannot be controlled by …………….
Ans: Water


Q3. Explain how the use of CNG in automobiles has reduced pollution in our cities.
Ans: 

  • Combustion of fuels like petroleum causes formation of un-burnt carbon particles along with carbon monoxide gas. These harmful pollutants enter the air and cause respiratory diseases. NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame
  • Compressed Natural Gas (CNG) produces these harmful products in very less quantity. It is a comparatively cleaner fuel. Therefore, the use of CNG has reduced pollution in our cities.


Q4. Compare LPG and wood as fuels.
Ans:NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame


Q5. Give reasons:
(a) Water is not used to control fires involving electrical equipment.
Ans: Water is a conductor of electricity, so it can easily conduct electric current and cause danger of electric shocks or short-circuits. Therefore, water can not be used to control the fire involving electrical equipment.

(b) LPG is a better domestic fuel than wood.
Ans: LPG is a better domestic fuel as it does not produce smoke and un-burnt carbon particles, which cause respiratory problems.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
Ans: Paper by itself catches fire easily because it has low ignition temperature but when wrapped around an aluminium pipe its temperature is lowered due to aluminium metal absorbing the heat supplied to paper. So it does not catch fire.


Q6. Make a labelled diagram of a candle flame.
Ans:

NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame


Q7. Name the unit in which the calorific value of a fuel is expressed.
Ans: The calorific value of a fuel is expressed in kilojoules per kilogram (kJ/kg).


Q8. Explain how CO2 is able to control fires.
Ans: Being heavier than oxygen, CO2 covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled.


Q9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Ans: Green leaves have a lot of moisture in them. This moisture does not allow them to catch fire easily. However, dry leaves have no moisture in them. Therefore, they catch fire easily.

Q10. Which zone of a flame does a goldsmith use for melting gold and silver and why?
Ans: A goldsmith uses the outer part of the candle flame for melting gold and silver because in this zone the temperature is the highest which helps to melt these metals easily.


Q11. 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
Heat produced by burning the given mass of fuel = 180,000 kJ.
We know that calorific value of fuel:

NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame

Hence, the calorific value of the given fuel = 40,000 kJ/kg.


Q12. Can the process of rusting be called combustion? Discuss.

Rusted Iron ObjectRusted Iron Object

Ans: Combustion is a chemical process in which a substance reacts with oxygen and gives out energy during the process in the form of either heat or light or both. Rusting of iron is an exothermic process as heat is released during rusting. Hence, it is a kind of slow combustion.


Q13. 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 in the Ramesh's beaker will heat up in a shorter time. This is because the outermost zone of a flame is the hottest zone, while the yellow zone (in which Abida had kept the beaker) is less hot.

The document NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame is a part of the Class 8 Course Science Class 8.
All you need of Class 8 at this link: Class 8
109 videos|302 docs|55 tests

Up next

FAQs on NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame

1. What is combustion?
Ans. Combustion is a chemical process in which a substance reacts with oxygen and releases energy in the form of heat and light. This process is also known as burning, and it is accompanied by the production of carbon dioxide and water vapor.
2. What are the different types of combustion?
Ans. There are three types of combustion: rapid combustion, spontaneous combustion, and slow combustion. Rapid combustion occurs with a sudden burst of flame and heat, while spontaneous combustion occurs without any external heat or flame. Slow combustion occurs when the fuel burns slowly over a long period of time.
3. What is a flame?
Ans. A flame is a visible, gaseous part of a fire that emits light and heat. Flames are created when combustible materials are heated to their ignition temperature and react with oxygen to produce a self-sustaining combustion reaction.
4. What are the different methods of extinguishing a fire?
Ans. There are several methods of extinguishing a fire, including smothering, cooling, and removing the fuel source. Smothering involves cutting off the oxygen supply to the fire, while cooling involves reducing the temperature of the fire by applying water or other coolants. Removing the fuel source involves removing the material that is burning.
5. What are the dangers of incomplete combustion?
Ans. Incomplete combustion can be dangerous because it can result in the production of toxic gases such as carbon monoxide. These gases can be harmful to humans and animals and can cause carbon monoxide poisoning. Incomplete combustion can also result in the production of soot and other particulate matter, which can be harmful to the environment and human health.
109 videos|302 docs|55 tests
Download as PDF

Up next

Explore Courses for Class 8 exam
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Download the FREE EduRev App
Track your progress, build streaks, highlight & save important lessons and more!
Related Searches

mock tests for examination

,

Objective type Questions

,

past year papers

,

shortcuts and tricks

,

Viva Questions

,

Exam

,

practice quizzes

,

NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame

,

NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame

,

video lectures

,

Important questions

,

Sample Paper

,

Extra Questions

,

MCQs

,

study material

,

Previous Year Questions with Solutions

,

NCERT Solutions for Class 8 Science Chapter 4 - Combustion and Flame

,

pdf

,

ppt

,

Free

,

Semester Notes

,

Summary

;