Combustion And Flame

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.

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 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

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.

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.

The main requirement for burning of any substance to continue is Oxygen. Without it, no substance can continue to burn. Thus, the flame extinguishes.

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.

Ignition temperature is the temperature at which a substance starts burning. Coal requires a very high initial temperature to start burning.

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.

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.

Calorific value of a substance is the amount of heat released when a substance is burnt completely. Its units are kJ/Kg.

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.

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.

A fuel that leaves away a lot of waste is not appreciated. They do not seem to be efficient.

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.

(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.

(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.

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.

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.

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.

(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.

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.

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.

(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

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.

(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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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