Q 1 – Name the most common fuel used in homes.
Ans. Liquefied Petroleum Gas. (LPG)
Q 2 – Name the most common fire extinguisher.
Ans. Water
Q 3 – What are the states in which a fuel may exist?
Ans. A fuel may exist in a solid, liquid, or gaseous state.
Q 4 – When any two combustible substances.
Ans. Charcoal, wood
Q 5 – Does magnesium produce heat and light during its combustion?
Ans. Yes, it does.
Q 6 – What acts as fuel for our body?
Ans. Food
Q 7 – Give two examples of non-combustible substances.
Ans. Water, sand
Q 8 – How are heat and light produced in the sun?
Ans. In the sun, heat and light are produced by nuclear reactions.
Q 9 – Where were matchsticks first used?
Ans. Egypt
Q 10 – What are the three essential requirements for combustion?
Ans. Fuel, air (to supply oxygen), and heat (to raise the temperature of the fuel beyond the ignition temperature
Q 11 – What is the ignition temperature of phosphorus?
Ans. 5°C
Q 12 – What is the color of an LPG flame?
Ans. Blue
Q 13 – What type of process is combustion?
Ans. A chemical process
Q 14 – Name an ideal fuel.
Ans. Compressed Natural Gas (CNG)
Q 15 – What is the composition of the head of a matchstick?
Ans. Antimony trisulphide and potassium chlorate.
Q 16 – Which part of a flame does a goldsmith blow for melting gold and silver?
Ans. The goldsmith blows the outermost zone of a flame for melting gold and silver.
Q 17 – What is the unit for expressing the calorific value of a fuel?
Ans. Kilojoules per kilogram (kJ/kg)
Q 18 – Comparing the calorific values of coal and petrol, state which fuel is better.
Ans. The calorific value of coal is about 25,000 – 33,000 kJ/kg, whereas that of petrol is 45,000 kJ/kg. Hence, petrol is better Fuel.
Q 19 – What is deforestation?
Ans. The cutting down of trees on a large scale is termed as deforestation.
Q 20 – Give any two examples of carbon fuels.
Ans. Coal, petroleum
Q 21 – What does magnesium burn to form?
Ans. Magnesium burns to form magnesium oxide and produces heat and light.
Q 22 – What does coal produce during its combustion?
Ans. Coal produces carbon dioxide, heat, and light during its combustion.
Q 23 – What is combustion?
Ans. Combustion is a chemical process in which a substance reacts with oxygen to give off heat.
Q 24 – Define the ignition temperature of the fuel.
Ans. The lowest temperature at which a fuel catches fire is called its ignition temperature.
Q 25 – How does a matchstick catch fire?
Ans. By rubbing a matchstick against a rough surface (friction), it attains its ignition temperature and thus catches fire.
Q 26 – What are combustible and non-combustible substances?
Ans. Substances that undergo combustion are said to be combustible, whereas non-combustible substances are those which don’t burn.
Q 27 – What are inflammable substances? Give examples.
Ans. The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances; e.g., LPG, petrol, alcohol, etc.
Q 28 – Define spontaneous combustion.
Ans. A type of combustion in which the substance suddenly catches fire without the supply of heat or friction externally is called spontaneous combustion; e.g., forest fires
Q 29 – Give two examples each of solid fuels, liquid fuels and gaseous fuels.
Ans.
- Solid fuels – Wood, cow dung, etc.
- Liquid fuels – Kerosene, petrol, etc.
- Gaseous fuels – Hydrogen, methane, etc.
Q 30 – Give two examples of fuels that are used to generate electricity.
Ans. Two examples of fuels that are used to generate electricity are petrochemicals and coal.
Q 31 – Define the dark zone of a flame.
Ans. The innermost zone of a flame around the wick is called its dark zone. It is the least hot zone comparatively to others.
Q 32 – Mention any three characteristics of a good fuel
Ans. Any three characteristics of a good fuel are following:
- It has high calorific value.
- It is very easy to transport.
- It is cheap, affordable and economic.
Q 33 – What is global warming?
Ans. An increase in the average temperature of the earth’s atmosphere, especially a sustained increase that causes climatic changes, is termed as ‘global warming.
Q 34 – Why isn’t hydrogen gas used as a domestic or industrial fuel, although it has a very high calorific value? State three reasons for the answer.
Ans. Although hydrogen gas has a very high calorific value, it is not used as a domestic or industrial fuel due to the following reasons:
- It is expensive.
- It burns with an explosion.
- It is extremely inflammable, so it is risky to store and transport hydrogen.
Q 35 – Explain how water gets boiled in the paper cup without burning it.
Ans. When we heat the paper cup containing water, the heat given to it is rapidly transferred to water from the paper cup. The temperature of the water goes on increasing until it attains its boiling point and starts boiling. As, during this process, the heat is continuously being transferred to water; the paper cup does not attain its ignition temperature. Hence, it does not burn.
Q 36 – Why does a piece of paper burn with yellow flame? Give a reason.
Ans. The inadequate supply of oxygen during the combustion of the piece of paper produces solid carbon particles that rise up in the flame. They become hot and glow to give off a yellowish light. This makes the piece of paper burn with a yellowish flame.
Q 37 – It is observed at petrol pumps and airports, that hydrocarbon fire extinguishers are used, instead of soda-acid fire extinguishers. Give reasons why.
Ans. At petrol pumps and airports, there is more probability of fire breaking out due to oil. In such situations, a soda-acid fire extinguisher does not work as it contains water or uses water to take off the fire by cooling down the place. Water being heavier than oil sinks to the bottom and hence, fire does not get controlled. In such a case, the hydrocarbon fire extinguisher is very useful, as it contains turkey red oil, which causes the foaming of carbon dioxide gas under pressure. The foam covers the surface of the burning substances and dispels the supply of air to control fire.
Q 38 – Explain complete combustion.
Ans. This type of combustion involves the complete burning of the combustible substance. No residue is left behind. Ash or smoke is not given off during or after this type of combustion. Most gases, such as hydrocarbons go through this form of combustion. On combustion, hydrocarbon produces carbon dioxide, water, and heat.
Q 39 – Write in brief about the reasons of forest fires.
Ans. Reasons for forest fires are:
- lightning if strikes forest trees or areas may lead to forest fires.
- human-caused fires.
- during extreme heat of summer, at some places dry grass catches fire. From this grass, very soon, it spreads to the whole forest.
- sparks from rock falls in a mountainous region can also be the reason of forest fires.
- volcanic eruption can also cause forest fires.
Q 40 – Can the process of cellular respiration be called combustion? Why?
Ans. Yes. Cellular respiration is a set of metabolic reactions and processes that breaks large molecules into smaller one with the release of heat. So, this is a slow combustion reaction.
Q 41 – 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?
Ans. We will observe that the iron wire will become red hot and start glowing but it will not produce a flame as it is a non-flammable object.