Define combustion.

Combustion is the process of burning of a substance in the presence of air or oxygen with the liberation of energy in the form of heat and light.

The conditions necessary for combustion are:
(1) Presence of combustible substance
(2) Supporter of combustion
(3) Attainment of ignition temperature 

Differentiate between combustible & non-combustible substances.

Combustible substances.
Those substances which burn easily are called combustible substances. for eg. Paper, petrol, LPG & wood etc.
Non-combustible substances.
Substances which do not burn in air or oxygen are called non-combustible substances. For eg. glass, sand, soil & cement.

Define ignition temperature ?
The lowest temperature at which a substance catches fire and starts burning is known as ignition temperature.

What are the different types of combustion ?

Combustion is mainly of three types:
1.Rapid combustion -If a combustion reaction takes place with a high speed &in which a large amount of heat & light are produced in a short time is called Rapid combustion. for eg. burning of matchstick, burning of magnesium ribbon.

2.Spontaneous combustion-A combustion which occurs on its own ,without the application of heat is called spontaneous combustion. For eg. Forest fire, burning of white phosphorus.

3. Explosion -The process of combustion where large amount of gases are evolved with the production of a tremendous amount of heat, light and sound is called explosion. for eg. Burning of crackers.

What is an incomplete combustion ?
Incomplete combustion of a substance takes place in the presence of insufficient amount of air or oxygen, this results in the formation of carbon monoxide, soot, heat &light.

What do you meant by inflammable substances?

The substance which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.

What is meant by the term ‘fuel’?

A fuel is a substance, which may be burnt to produce considerable heat without the formation of objectionable products.

What are the characteristics of an ideal fuel ?

An ideal fuel should have the following characteristics:
1.It should have a high calorific value.
2. It should not produce any harmful products on burning.
 3. It should cause minimum pollution of air.
4. It should be cheap and readily available.
 5. It should be easy to store,transport and handle.
 6. Its ignition temperature should be above the room temperature.
7. It should leave no residue after burning.
 8. It should burn at a moderate rate.

Define Calorific value of a fuel ?
The amount of heat produced on complete combustion of one kg of a fuel is known as its calorific value.It is usually expressed in kilojoule per kg (kj/kg).

How is a flame produced?
A flame is said to be produced when a combustible substance is in the vapour state & burns.

What are the different zones of a candle flame ?
different zones of a candle flame
zones of a candle flame 

A candle flame consists of three zones

1.Non-luminous zone or zone of complete combustion.
2.Luminous zone or zone of incomplete combustion.
3. Dark zone or zone of no combustion.

What is Acid rain .Explain its consequences.
Burning of coal and diesel releases sulphur dioxide gas &oxides of nitrogen which when dissolved in rainwater produces the acid rain.It is quite harmful for crops,buildings and soil. These gases also cause respiratory problems like asthma and bronchitis.

The gases like nitrogen oxide, sulphur dioxide etc. present in the atmosphere as pollutants when these gases dissolve in rain water and form acids and reaches to the earth as rain called as acid rain.

What is Green house effect ? explain its consequence ? 
An increase in the concentration of carbon dioxide in the atmosphere leads to an increase in the temperature of the earth is called GREENHOUSE EFFECT.

Its consequences are melting of polar ice ,raising the level of water in seas and oceans.This would cause flooding and submerging of many low lying areas.

Explain the term’ global warming’.         

The combustion of fuels release carbondioxide in the environment. When the percentage of carbondioxide increases in the air and makes the earth surface hot – it is believed to cause global warming.

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