A Journey into the Chemistry, Heat, and Illumination of Fire

Combustion is a chemical reaction between a fuel and an oxidizing agent, typically oxygen, resulting in the release of heat and light. Flames are characteristic of various processes, serving as visible indicators of the release of energy through chemical reactions.

What is Combustion: Ignition, Fuel, and the Essential Conditions for Flames

• Meaning: Combustion is a chemical process where a substance reacts with oxygen to produce heat. 
  • The burning substance is termed combustible or a fuel, which can be solid, liquid, or gas.
• Emission of Light: During combustion, light may also be emitted either as a flame or a glow.
• Burning of Magnesium: Magnesium, when burned, forms magnesium oxide while releasing heat and light. 
  • Charcoal, like coal, burns in air producing carbon dioxide, heat, and light.
• Human Body: In our bodies, food reacts with oxygen to produce heat, serving as a fuel.

• Conditions for Combustion:

• • Air is essential for combustion.
  • Candle Burning: A candle burns freely when there’s a flow of air but flickers and produces smoke or goes off entirely when the air supply is restricted.
  • Fire Extinguisher: Fire can be extinguished by cutting off the air supply, as seen when a burning person is covered with a blanket.

• Ignition Temperature:
  • Meaning: Different substances have distinct temperatures at which they catch fire, known as their ignition temperature.
    • Example: A matchstick doesn’t ignite at room temperature but does when friction is applied by striking it against the matchbox.
  • Design of Matchstick: The design of the matchstick has evolved, with the current safety matches containing safer chemicals than their earlier counterparts, which had dangerous white phosphorus.
  • A combustible substance won’t burn if its temperature remains below its ignition temperature. 
    • This is why cooking oil might catch fire on prolonged heating but wood doesn’t. 
  • Ignition temperature ensures substances only burn when they reach a certain temperature.
    • Example:  A paper cup not burning when it contains water since the water prevents the paper from reaching its ignition temperature.

• Inflammable Substances:
  • These are substances with very low ignition temperatures, making them easily catch fire.
    • Examples: Petrol, alcohol, and Liquified Petroleum Gas (LPG).

Diverse Facets of Combustion: Rapid, Spontaneous, and Explosive Phenomena exposed

• Rapid Combustion: When substances burn swiftly and produce heat and light. 
  • Example: when a burning matchstick or gas lighter is brought near a gas stove, the gas burns rapidly, exemplifying rapid combustion.

• Spontaneous Combustion: This refers to a type of combustion where a material spontaneously bursts into flames without any apparent external cause.
  • Substances like phosphorus can ignite in air at room temperature.
  • Instances include coal dust causing fires in coal mines due to spontaneous combustion.
  • Natural causes like sunlight or lightning can lead to spontaneous forest fires. 
  • However, human negligence, such as leaving campfires unextinguished, is often the major cause of forest fires.

• Explosion: An explosion occurs when a sudden reaction results in the rapid release of heat, light, sound, and gas. 
  • Example: Fireworks during festivals. When a cracker is ignited, it leads to an explosion.
  • External pressure applied to a cracker can

Flame Diversity: Colors, Vaporization, and Zones 

• LPG flame and candle flame have distinctive colours. 
• Substances that evaporate during burning form flames. 
  • Example:  Kerosene and molten wax.
• Charcoal doesn’t produce a flame as it doesn’t vaporise.
• The luminous zone of a flame indicates the presence of unburnt carbon particles.
• The non-luminous zone is the hottest part of the flame, often used by goldsmiths for melting precious metals due to its high temperature.