Combustion and its Types

Combustion

The chemical process of burning of a substance in the presence of air or oxygen with the liberation of heat and light is called combustion. Substances can be classified as:

Combustible substances: Substances that burn in air or oxygen to produce heat and light are called combustible substances. E.g. paper, wood, kerosene, LPG.

Non combustible substances: Substances that do not burn in air or oxygen to produce heat and light are called non- combustible substances e.g.: water, sand, glass etc.

Types of combustion:

1. Rapid combustion: larger amount of heat and light are released in a very short span of time. E.g. combustion of LPG, which produces heat light intently. They also require external heat. Cooking gas (in our homes), spirit, petrol and camphor go to flames even with a spark from gas lighter. These materials are highly inflammable. You might have observed "Highly Inflammable " written on petrol tankers. This is a warning to keep a flame away from these tankers.

2. Explosion: Characterized by sudden release of heat, light and sound e.g.: bursting of firecrackers.When a cracker is ignited it explodes with a big -bang producing heat and light (sparkles.) Same is the true with the firing of gun. Big sound is produced along with combustion. Fire wood burns with a crackling sound.

3. Spontaneous combustion: Substances catch fire on their own, without the application of external heat e.g. white phosphorous.In this type of combustion a material suddenly bursts into flames without the application of any apparent cause for e.g. spontaneous forest fires are sometimes due to the heat of the sun or lighting strike.

Combustion of hydrocarbons can be divided in to two types :-

1. Complete combustion: Combustion takes place in adequate amount of air or oxygen. It results in the formation of carbon dioxide, water, heat and light.

2. Incomplete combustion: Combustion take place in inadequate amount of air or oxygen .It result in the formation of carbon monoxide, soot, water, heat and light.

Soot : Black powdered substance produced on incomplete combustion.

Condition necessary of combustion:

1. Presence of combustion substances: Combustion is only possible in the presence of combustion substance i.e. called fuel. e.g. wood, charcoal, petrol etc.

2. Presence of a supporter of combustion: Adequate amount of supporter of combustion e.g.: oxygen.

3. Attainment of ignition temperature: A substance start to burn after attainment of certain minimum temperature. The temperature at which a particular substances burn in the presence of air is called ignition temperature. A substance cannot catch fire below its ignition temperature.

Note: A substance will not burn without one or more of these conditions.

Inflammable substances: Substances like petrol, LPG, alcohol catch fire easily because they have low ignition temperature and are inflammable substances.

Combustion is a chemical process in which a substance (fuel) burns in the presence of air (oxygen) with the release of heat and light. On combustion the burning fuels gets combines with oxygen to form new substance. Sometimes, combustion is accompanied with the production of sound as well.The sound produced may be a hissing sound, crackling sound or an explosion.

$large C +O_2 rightarrow CO_2 + Heat$ `

When compounds undergo combustion, two or more combustion products are formed. When carbon - hydrogen compounds undergo combustion is an excess of oxygen, the combustion products are carbon dioxide and water.

$large CH_{4}(g)+2O_{2}(g)rightarrow CO_{2}(g)+2H_{2}O(l)$

The metabolism of glucose $large C_{6}H_{12} O_{6}$ , blood sugar that occurs in our bodies the energy to sustain our life is also a combustion reaction that occurs at a steady rate

$large C_{6}H_{12} O_{6}left ( aq right )+6O_{2}(g)rightarrow 6CO_{2}(g)+6H_{2}O(l)$

Sample Questions

(More Questions for each concept available in Login)

Question : 1

Digestion of food is in an example of __________________
A. Incomplete combustion	B. Complete combustion	C. Slow combustion	D. Rapid combustion
Right Option : C
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Question : 2

The products of combustion are ________________
A. Oxygen and water	B. Carbon dioxide and water	C. Only carbon dioxide	D. Only oxygen
Right Option : B
View Explanation

Question : 3

Which of the following mixture is used as a catalyst for cracking of hydrocarbons ?
A. Mixture of silica and alumina		B. Mixture of silicon and ammonia
C. Mixture of nickel and silica		D. Mixture of platinum and silica
Right Option : A
View Explanation