COMBUSTION AND FLAME

INTRODUCTION

A chemical process in which a substance reacts with oxygen to give off heat terms as combustion. In combustion and flame we come to know that the substance that undergoes combustion is we know as combustible. It is also called fuel which can be solid, liquid or gas. During combustion, sometimes light evolves as a flame e.g. when coal, wood, magnesium are burnt these produce heat and light.

NECESSARY CONDITIONS FOR COMBUSTION IN COMBUSTION AND FLAME

Occurrence of a combustible substance.
Presence of a supporter of combustion.
Heating of a combustible substance to its ignition temperature or attainment of ignition temperature.

COMPARATIVE STUDY OF VARIOUS SUBSTANCES

COMBUSTIBLE SUBSTANCE	NON-COMBUSTIBLE SUBSTANCE	INFLAMMABLE SUBSTANCE
The substances which burns in air or oxygen	This does not burn in air or oxygen	The substance which has very low ignition temperature and can catch fire easily with a flame
e.g. petrol, paper, kerosene	e.g. water, glass, sand	e.g. petrol, alcohol, LPG

SUPPORTER OF COMBUSTION:

A substance which helps in combustion is called a supporter of combustion e.g. oxygen, air etc.

IGNITION TEMPERATURE:

Before a substance catches fire and starts burn, we must heat the substance to a certain minimum temperature by supplying heat. The lowest temperature at which a substance catches fire and starts burning terms as ignition temperature. A combustible substance cannot catch fire if its temperature is lower than its ignition temperature.

HOW DO WE CONTROL FIRE IN COMBUSTION AND FLAME

COMBUSTION AND FLAME: We have learnt that there are three essential requirements for producing fire. If anyone can remove any of these three things then the burning procedure will stop and fire extinguishes. Thus Fire extinguishing procedure are of three types:

By removing the fuel, but in most cases, fuel cannot be eliminated.
if we remove the heat.
By cutting off the air supply to the burning substances.

TYPES OF FIRE EXTINGUISHER:

WATER: It is the most common fire extinguisher. But we can be use it only in fire on paper and wood. Water extinguishes fire by cooling the burning substances.
CARBON DIOXIDE (in liquid form) : It extinguishes fire arising from electrical equipment and inflammable substances like petrol, kerosene etc. CO₂ is denser than air and thus forms a layer around the burning substance. This gas covers the fire like a blanket so that fresh air cannot reach the burning substance.
CARBON DI OXIDE ( in the form of dry powder of baking soda and potassium bicarbonate) When we release this powder through extinguisher machine , it reduces the heat released by the fire.

TYPES OF COMBUSTION

There are various types of combustion. three important types of combustion are:

RAPID COMBUSTION : In this combustion in short time large amount of heat and light evolve , like burning of cooking gas (LPG) in a gas stove.
SPONTANEOUS COMBUSTION: It occurs on its own without the help of any external heat, like burning of white phosphorus in air at room temperature.
EXPLOSIONS: It is a sudden combustion resulting formation of a large amount of heat, light and sound are ,like bursting of cracker.

PROBLEMS RELATED TO COMBUSTION AND FLAME:

Qs1 As a result of incomplete combustion which harmful gas evolves?

Ans1 Carbon monoxide which is a poisonous and harmful gas evolves as a result of incomplete combustion.

Qs2 Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed natural Gas (CNG) in big cities?

Ans2 It is because CNG produces harmful pollutants in very small amount, so, it is a clean fuel.

ANSWER IN BRIEF ON COMBUSTION AND FLAME)

Qs3 How heat is produced in our body?

Ans3 In our body, food is broken down by reavtion with oxygen. During such reactions, heat is produced, this heat keeps our body warm.

Qs4 Name two fuels which we use in our homes for cooking food?

Ans4 Two fuels which we use in our homes for cooking food are LPG and kerosene oil.

GIVE REASONS ON COMBUSTION AND FLAME

Qs5 Which type of fuel produces flame? Does charcoal burn with flame?

Ans5 The substances which vaporise during burning produce flame.

No, charcoal does not burn with flame, it glows only because it does not vaporise on burning.

Qs6 Do all substances catch fire at the same temperature?

Ans6 No, all the substances do not catch fire at the same temperature. Different substances need different temperature to catch fire which is called ignition temperature.

HIGHER ORDER THINKING SKILL

Qs7Like fuels, the sun also provides heat and light. What is the source of heat and light in the sun?

Ans7 In the sun, nuclear reaction takes to produce heat and light .

SHORT TYPE QUESTION

Qs8 When combustion takes place what are the products?

Ans8 The products of combustion are carbon dioxide, water vapour, heat and light.

Qs9 Why do we cover a with a blanket when the clothes of that person catch fire?

Ans9 When the clothes of a person catch fire, we must cover the person with a blanket for extinguishing the fire. This is because the supply of air to the burning clothes cut off by blanket. Due to which the clothes stop burning and fire gets extinguished.

EXPLAIN THE FOLLOWING ON COMBUSTION AND FLAME

Qs10:We know that wood contains large amount of calorific value, we still discourage its use as a fuel. Explain.

Ans10: Burning of wood has several disadvantages in combustion and flame. These are as follows:

By burning wood huge amount of smoke is produced which causes respiratory diseases.
We use to cut down trees to get wood which we use as fuel. This activity leads to deforestation which is very harmful to the environment.
Trees provide us many useful substances. But deforestation reduces our naturel resource like wood.

Qs11: A girl Manu heated oil for frying aloo chips. Suddenly oil catches fire, she poured water to extinguish the fire. Do you think, this action was suitable? If yes, why? If not, why not? What should be her duty in thius dangerous condition?

Ans11: If she pours water to extinguish fire it will be worst condition. It is because oil is lighter than water. So, water will settle down below the oil. In this case Manu should use sand or soil. That sand or soil can cut off the air supply to the fire. Thus, fire can be controlled. But sometime we cannot get sand or soil easily.

So, Manu must switch off the burner and put a lid on the frying pan. When Manu will do this activity, the contact between fuel and oxygen is disconnected, followed by putting off of flame.

COMBUSTION AND FLAME: HOW TO SAVE ENERGY IN ITS