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Showing 2 questions in Chemistry for Class 8. Tap a card to reveal the answer.
ChemistryCombustion and FlamemediumWhat three conditions are necessary for combustion to take place?
Reveal answer ↓
What it is
Burning needs three partners together: fuel, oxygen and enough heat.
Answer
For combustion, three things must be present together: a combustible substance (fuel), a supporter of combustion (usually oxygen from air) and heat to raise the fuel to its ignition temperature. If any one is removed, burning stops - which is why covering a fire with a blanket (cutting off oxygen) or water (cooling below the ignition temperature) puts it out.
- •Fuel (combustible substance)
- •Oxygen (supporter of combustion)
- •Heat to reach ignition temperature
- •Remove any one -> burning stops
Why learn this
It's exactly how firefighters put out fires - remove any one partner and the fire dies.
💡 Memory trick
Fire Triangle: Fuel + Oxygen + Heat. Break one side, break the fire.
ChemistryCombustion and FlamemediumWhat are the characteristics of a good fuel?
Reveal answer ↓
What it is
A good fuel gives lots of heat, is cheap, easy to store and burns cleanly.
Answer
A good fuel should have a high calorific value (release a large amount of heat per kilogram), a moderate ignition temperature, be readily available and cheap, be easy to store and transport, and burn without leaving much ash or releasing harmful smoke. For example, LPG is a good domestic fuel because it has a high calorific value and burns cleanly.
- •High calorific value (much heat per kg)
- •Moderate ignition temperature, cheap, available
- •Easy to store and transport, little ash or smoke
Why learn this
It's how we choose cooking gas, vehicle fuel and industrial fuel - and cut pollution.
💡 Memory trick
A good fuel: high Calorific value, Cheap, Clean, easy to Carry - the four C's.