A substance which reacts with oxygen giving heat is called a combustible substance. Which, one of the following is a combustible substance?
A. iron nail
B. glass
C. stone piece
D. wood
A substance that has the ability to produce smoke when it is heated is known is known as a combustible substance. Iron, glass and stone piece do not react with oxygen to give heat. Thus, wood is the right answer.
Which one of the following has the highest calorific value?
A. kerosene
B. biogas
C. LPG
D. petrol
Calorific represents the amount of heat generated when a fuel burns completely. The energy released when LPG is burnt is 55000 kJ/Kg. It is the highest when compared to the others.
Magnesium ribbon on burning in air produces
A. magnesium oxide, water and light
B. magnesium oxide and heat
C. magnesium oxide, heat and light
D. magnesium oxide, water and heat
Magnesium is a highly reactive metal. When it is exposed to Oxygen, it reacts immediately to give Magnesium Oxide (MgO), heat that gives light.
The equation of the reaction is as follows:
Mg + O2→ MgO + Heat + Light
Which of the following is not a combustible substance?
A. camphor
B. glass
C. straw
D. alcohol
A substance that does not react with oxygen in air and does not produce heat is known as a non-combustible substance. Camphor, straw and alcohol react vigorously with fire. No such reaction takes place in the case of glass.
The substance that does not burn with flame is
A. LPG
B. camphor
C. dry grass
D. charcoal
When LPG, or dry grass, or camphor are burnt, they vaporize and thus a flame is generated. But, in the case of Charcoal, no flame is produced. So, it doesn’t give a flame.
On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is because of non-availability of
A. oxygen
B. water vapors
C. carbon dioxide
D. wax
The main requirement for burning of any substance to continue is Oxygen. Without it, no substance can continue to burn. Thus, the flame extinguishes.
If a person’s clothes catches fire, the best way to extinguish the fire is to:
A. throw water on the clothes.
B. use fire extinguisher.
C. cover the person with a woolen blanket.
D. cover the person with a polythene sheet.
To extinguish the fire, its root cause has to be solved. That is, the availability of oxygen should be reduced. This can be done by wrapping a blanket around the person.
The substance expected to have the highest ignition temperature out of the following is
A. kerosene
B. petrol
C. coal
D. alcohol
Ignition temperature is the temperature at which a substance starts burning. Coal requires a very high initial temperature to start burning.
Choose the correct statement about inflammable substances from the following. They have:
A. low ignition temperature and cannot catch fire easily.
B. high ignition temperature and can catch fire easily.
C. low ignition temperature and can catch fire easily.
D. high ignition temperature and cannot catch fire easily.
Inflammable substances are those which can catch fire easily and are very dangerous. A slight temperature can be enough for them to get ignited. An example for inflammable substance is Petrol.
Choose the incorrect statement from the following. Forest fires are usually due to:
A. carelessness of humans
B. heat of sun
C. cutting of trees
D. lightning strike
Forest fires occur because of the rise in temperature in the particular area. Wood catches fire easily and thus, the entire forest is burnt. Cutting of trees does not produce heat.
The calorific value of a fuel is expressed in a unit called
A. kilojoule per litre
B. kilogram per mililitre
C. kilojoule per gram
D. kilojoule per kilogram
Calorific value of a substance is the amount of heat released when a substance is burnt completely. Its units are kJ/Kg.
In villages, people use wood as fuel because:
A. it is considered to be an ideal fuel.
B. of its easy availability and low cost.
C. it is environment friendly.
D. it catches fire easily.
In villages, there is lack of resources. But, wood is present in bulk. So, using wood as a source of fuel is considered to be economical as it is easily available and economical.
Which among the following is considered as the cleanest fuel?
A. cow dung cake
B. petrol
C. kerosene
D. hydrogen gas
Hydrogen gas on combustion does not produce any harmful gases which is not the case with kerosene, cow dung and petrol. Thus, it is considered to be a very clean fuel.
Choose the incorrect statement from the following.
A good fuel is one which:
A. is readily available.
B. produces a large amount of heat.
C. leaves behind many undesirable substances.
D. burns easily in air at a moderate rate.
A fuel that leaves away a lot of waste is not appreciated. They do not seem to be efficient.
Shyam was cooking potato curry on a chulha. To his surprise he observed that the copper vessel was getting blackened from outside. It may be due to:
A. proper combustion of fuel.
B. improper cooking of potato curry.
C. improper combustion of the fuel.
D. burning of copper vessel.
When a fuel is not burnt properly, a lot of soot is left over. This is black in color. Copper is a metal and it also reacts with oxygen easily.
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.
(e) The substances which vapourise during __________, give flame.
(a) Chemical and Oxygen
Combustion takes place only in the presence of Oxygen.
(b) Fire and Blanket.
A blanket helps prevent oxygen from entering into the cloth which is on fire, and thus helps prevent fire.
(c) Lowest and Ignition.
The minimum temperature at which a substance catches fire is known as the Ignition Temperature.
(d) Low and Inflammable.
Low ignition temperature implies that the substance can catch fire as soon as it is exposed to it. This temperature is known as Ignition Temperature.
(e) Burning
On heating a substance, it produces fire. A flame is produced when a substance is burnt.
Some words (underlined) in the following sentences are jumbled up. Write them in their correct form.
(a) Seldie is a combustible substance.
(b) Slags is a non-combustible material.
(c) Chittsmack does not burn by itself.
(d) Some substances on combustion produce thea and mafel.
(e) The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its ficalroic value.
(a) Diesel is a combustible substance.
Because it has an ability to catch fire very easily.
(b) Glass is a non-combustible material.
Because it does not catch fire.
(c) Matchstick does not burn by itself.
Because, its temperature is less than the ignition temperature.
(d) Some substances on combustion produce heat and flame.
Substances react with Oxygen and give heat and light.
(e) The amount of heat energy produced on complete combustion of 1Kg of a fuel is called its Calorific value.
Calorific value determines the efficiency of a fuel.
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?
The jar will remain lighted for a longer time in jar B. This is because, air (specifically, Oxygen) is a supporter of combustion. Thus, without oxygen, combustion cannot take place.
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.
The outermost layer of the flame is the hottest part. So, if she wants to boil the water quickly, she will have to keep the test tube at the outermost layer.
Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed Natural Gas (CNG) in big cities?
Fuels like petrol and diesel give away a lot of smoke when heated, thus causing pollution. CNG is an environment friendly fuel and does not play a role in the increase of pollution. CNG produces harmful products in a very small quantity.
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.
(a) Combustible substances — charcoal, straw, card board, paper, candle wood,
(b) Non-combustible substances — chalk, stone, iron rod, copper coin, glass.
Substances that catch fire easily are known as combustible substances.
Substances that do not catch fire easily are known as non-combustible substances.
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.
Statement (a) is correct.
Air consists of oxygen which is a necessity for ignition.
Statement (b) is wrong. The correct statement is - Magnesium is a combustible metal.
Magnesium has an ability to catch fire and thus burn easily. It burns as soon as it is ignited.
Statement (c) is correct.
Carbon di oxide helps extinguish fire by taking away the oxygen, thus making it difficult for the substance to continue to burn.
(d) is wrong. The correct statement is - Calorific value of coal is higher than that of wood.
More Calorific value of Coal represents that coal is more efficient than wood.
Match the items of Column A with the items of Column B.
Match the following for the flame of a candle.
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?
When we hold the piece iron wire with a pair of tongs inside a candle flame or a Bunsen burner flame of, the piece of iron will turn red hot and glow. It will not produce a flame as it doesn’t vaporize during burning. Any substance that has an ability to vaporize during burning can produce a flame.
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 __________.
(a) Combustion
It is a process where a substance reacts with oxygen and gives off heat.
(b) Combustible
A substance that can catch fire easily is called combustible substances. Examples include wood, paper etc.
(c) Ignition
The lowest temperature at which a substance catches fire is called its ignition temperature.
(d) Petrol
Petrol is an inflammable substance
(e) Ignition, Inflammable
(f) calorific value
People usually keep Angethi/burning coal in their closed rooms during winter season. Why is it advised to keep the door open?
In a closed room, there is a limited supply of oxygen. Availability of oxygen in a less quantity leads to the formation of Carbon mono oxide that is a highly poisonous gas and it can also kill the people sitting in the room.
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 vaporize during burning, give flame.
(a) False
A chemical process in which a substance reacts with oxygen to give off heat is called combustion. It is basically the process of burning any substance.
(b) False
Carbon dioxide is the best extinguisher for fires involving electrical equipment.
(c) True.
This is because, Carbon dioxide has an ability to remove the oxygen from the substance, thereby reduce combustion.
(d) False
Increased concentration of carbon dioxide in air is believed to cause global warming.
(e) True.
Carbon dioxide acts as a pollutant. It is a green house gas.
(f) False
The outer zone is the hottest zone of a flame.
(g) True.
Cracker on ignition produces sound. Why?
On the ignition of a cracker, a very fast reaction takes place that leads to the evolution of various gases. The gases expand very rapidly and thus, give off a lot of heat and sound.
What do you understand by fuel efficiency?
A fuel that produces a large amount of heat per unit mass can be considered t be the best fuel. That is, the fuel efficiency is the calorific value – The amount of heat released when 1Kg of the fuel.
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?
The watch glass containing petrol will catch fire the most easily because, petrol is an inflammable substance and its ignition temperature is also low. On the other hand, milk and mustard oil is not an inflammable substance. A substance is said to be inflammable if it has an ability to catch fire very easily.
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?
Water cannot extinguish fires containing oil. Thus, this action of his is not suitable. In such a condition, Manu should have switched off the flame of the burner and put a lid on the frying pan. By doing this the contact between fuel and oxygen is cut off and the flame will go off.
What are the three essential requirements to produce fire? How fire extinguisher is useful for controlling the fire.
The three essential requirements to produce fire are:
1) Fuel,
2) Air (Oxygen),
3) Heat for reaching the ignition temperature.
A fire extinguisher is used for extinguishing fires that are related to electrical appliances or petrol. It cuts off the supply of air to bring down the temperature of the fuel or both.
Give two examples each for a solid, liquid and gaseous fuel along with some important uses.
The examples of each solid, liquid and gaseous fuel are given as:
1) Solid Fuel: Coal, Wood - They are used for cooking purposes. Coal is also used in industries sometimes.
2) Liquid Fuel: Kerosene, Petrol – They are used as fuels in automobiles. Kerosene is also used in lamps.
3) Gas fuel: CNG, LPG – LPG is used as a fuel for industries.
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?
I would prefer a vehicle that runs on CNG. CNG has a higher calorific value, meaning – the amount of heat released when 1Kg of a substance is burned. So, its efficiency is also high when compared to that of petrol. Moreover, CNG is also economic and produces lesser harmful products.
Although wood has a very high calorific value, we still discourage its use as a fuel. Explain.
Though wood has a high calorific value, still it is not considered as a fuel because of the following reasons:
1) Burning of wood produces a lot of smoke which leads to pollution and is also harmful to the living beings.
2) Cutting down of wood leads to deforestation which in turn affects the environment.
3) Wood also has a very low calorific value.
4) It is also very costly.
Forest fire produces a lot of air pollution. Write in brief about the reasons of forest fires.
The reasons for forest fires are as follows:
1) Sometimes, when it is too hot, the dry grass may catch fire and thus would lead to the destruction of the entire forest.
2) Camp fires may also be a reason for the production of air pollution.
3) Human negligence is yet another factor that causes air pollution.
4) Natural causes like lightening may also be the reason for causing forest fires.
Complete the crossword Fig. 6.1 with the help of the clues:
Across
1. Non-metal which catches fire if exposed to air (10) oxygen to give off heat. (10)
3. The lowest temperature at which a substance catches fire is called its __________temperature. (8)
5. The most common fire extinguisher. (5)
Down
2. A chemical process in which a substance reacts with
4. Petrol is used as a __________ in automobiles. (4)
6. It is as hard as stone and black in color. (4)
Across:
1.Phosphorous – It catches fire in the presence of oxygen.
3.Ignition
5.Water – It can help extinguish fires. It is easily available.
Down:
2.Combustion
4. Fuel
5. Coal