Important Questions for Class 8 Chapter 6 - Combustion and Flame

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Important questions based on NCERT syllabus for Chapter 6 - Combustion and Flame:

Question-1: Give examples of substances which do not burn. Why do they not burn?

Solution: Glass, concrete, mud, carbon dioxide and water are example of some substances which do not burn. These substances are also called non-combustible substances.

These substances are non-combustible since they have very less affinity for oxygen and hence do not react with oxygen which is required for a combustion reaction.

Question-2: Give examples of substances which burn to give a flame. Why do some substances burn without a flame?

Solution: Candle, wood and paper are examples of some substances which burn with a flame. Whether a substance burns along with the evolution of flame depends on the amount and nature of energy released. If the released energy falls in our visible spectrum, we see a flame and when the energy does not fall in the visible spectrum, we do not see the flame.

Question-3: Define fuel efficiency.

Solution: Different types of fuels generate different amounts of heat. The heat produced by fuels is measured and expressed through its calorific value. For a fuel to be categorized as a good fuel, it should have a high calorific value, in other words greater is the calorific value larger is the amount of heat produced on burning that fuel and vice versa. So fuel efficiency may be defined as the amount of energy released per unit mass of the fuel.