Combustion & Flame Notes

• A chemical process in which a substance reacts with oxygen producing heat is called combustion.
• Substances can be classified as combustible or non-combustible, depending on whether or not they can be burnt.

Combustible substance:

• Substances which burn in air to produce heat and light are called combustible substances.
• E.g.:- wood, coal, charcoal, kerosene, petrol, diesel, liquified petroleum gas (LPG), compressed natural gas (CNG) etc.

• Complete combustion needs a plentiful supply of air so that the elements in the fuel react fully with oxygen.
• Fuels such as natural gas and petrol contain hydrocarbons. These are compounds of hydrogen and carbon only. When they burn completely:
• Carbon oxidises to carbon dioxide
• Hydrogen oxidises to water - Water, H₂O, is an oxide of hydrogen

General reaction for complete combustion:

• A substance will not burn without one or more of these conditions. 
• Combustible substance: Fuel
• Air (to supply oxygen)
• Heat (to raise the temperature beyond the ignition temperature)

Ignition temperature: