Current Affairs 8th Class

Category : 8th Class

Combustion and Flame

·                     Combustion is a process in which a substance reacts with oxygen to give off heat and light.

·                     The substances which burn in air are called combustible substances while those that do not burn easily are called non-combustible substances.

·                     The conditions required for combustion to take place are:

·                     The lowest temperature at which a combustible substance catches fire is called its ignition temperature.

·                     Inflammable substances have very low ignition temperature.

·                     Slow combustion, rapid combustion, spontaneous combustion and explosion are the different types of combustion.

§  Slow combustion: This type of combustion takes place at low temperatures. Respiration is an example of slow combustion.

§  Rapid combustion: in this type of combustion, the gas burns rapidly and produces heat and light.

§  Spontaneous combustion: in this type of combustion a material suddenly bursts into flames, without the application of any apparent cause.

§  Explosion: In this type of combustion; a sudden reaction takes place with the evolution of heat/ light and sound. A large amount of gas is also liberated in this reaction.

·                     A fire can be controlled either by cutting off the supply of oxygen or by removing the combustible substance.

·                     Water is commonly used to control fires but it cannot be used to control fires caused by chemicals that react violently with water, electrical equipment?s or oils.

·                     Carbon dioxide is used to extinguish the fire caused by electrical equipment or chemicals.                                                                    

·                     A flame has three different zones - dark zone, luminous zone and non-luminous zone.                                                                   

·                     A fuel that is cheap, readily available, readily combustible and easy to transport is called an ideal fuel. Such fuel is expected to have high calorific value. It does not produce gases or residues that pollute the environment.                           

·                     Fuel efficiency is expressed by calorific value. The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. The calorific value of a fuel is expressed in kilojoule per kg (kJ/kg). Fuels differ in their efficiency and cost.    

·                     Unburnt carbon particles in air are dangerous pollutants causing respiratory problems.

·                     Incomplete combustion of a fuel gives poisonous carbon monoxide gas.

·                     Global warming and acid rain are some of the harmful effects of combustion of fuels. Increased percentage of carbon dioxide in air leads to global warming. While oxides of Sulphur and nitrogen produced by the burning of coal, diesel and petrol cause acid rain which is harmful for crops, buildings and soil.