Chemistry - Combustion and Flame

Introduction

• A chemical process in which a substance reacts with oxygen and give off heat is known as combustion.

• The substance that undergoes combustion is called as combustible or fuel.

• The fuel can be in the form of solid, liquid, or gas.

• During the combustion, light is also given off either in the form of a flame or as a glow.

• The substances which vaporize during burning time, give flames.

• There are three different zones of a flame dark zone, luminous zone and non-luminous zone.

• Different substances catch fire at different temperatures.

• The lowest temperature at which a substance catches fire is known as its ignition temperature.

• A match contains antimony trisulphide and potassium chlorate.

• The rubbing surface of match contains powdered glass and a little red phosphorus.

• Red phosphorus is much less dangerous.

• When the match stick is struck against the rubbing surface, some red phosphorus gets converted into white phosphorus; the process immediately reacts with potassium chlorate present in the matchstick head and produce enough heat to ignite antimony trisulphide; likewise, combustion starts.

• The substances, which have very low ignition temperature and can easily catch fire with a flame, are known as inflammable substances. E. g. petrol, alcohol, Liquified Petroleum Gas (LPG), etc.

Fire Extinguisher

• Water is the most common fire extinguisher.

• Water, as fire extinguisher, works only when things like wood and paper are on fire.

• If electrical equipment is on fire, water may conduct electricity and damage those trying to douse the fire.

• Water is also not a good extinguisher for fires involving oil and petrol.

• For fires that involve electrical equipment and inflammable materials such as petrol, Carbon Dioxide (CO2) is the best extinguisher.

• One of the ways to get CO2 is to release plenty of dry powder of chemicals such as sodium bicarbonate (baking soda) or potassium bicarbonate.

• Phosphorus burns in air at room temperature.

• The amount of heat energy produced on complete combustion of 1 kg of a fuel is known as its calorific value.

• The calorific value of a fuel is measured in a unit called kilojoule per kg (kJ/kg).

• The following table illustrates the Calorific Values of Different Fuels −

• Combustion of most fuels releases carbon dioxide in the environment.

• Increased concentration of carbon dioxide in the air is most likely causes global warming.

• The rise in temperature of the atmosphere of the earth is known as Global Warming.

• Global warming causes melting of polar glaciers, which leads to a rise in the sea level that ultimately causing floods in the coastal regions.

• Oxides of sulphur and nitrogen dissolve in rain water and form acids; such type of rain is known as acid rain.