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Meaning:
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- 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.
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Emission of Light:
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- During combustion, light may also be emitted either as a flame or a glow.
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Burning of Magnesium:
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- Magnesium, when burned, forms magnesium oxide while releasing heat and light.
- Charcoal, like coal, burns in air producing carbon dioxide, heat, and light.
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Human Body:
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- In our bodies, food reacts with oxygen to produce heat, serving as a fuel.
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Conditions for Combustion
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- 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.
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Ignition Temperature
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- 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.
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Inflammable Substances
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- These are substances with very low ignition temperatures, making them easily catch fire.
- Examples: Petrol, alcohol, and Liquified Petroleum Gas (LPG).
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