Note the following experience.
- 1 cup;
- 2 candles;
- 1 box of matches.
- light both candles;
- cover one of the candles with a glass;
What keeps the candle flame lit is the oxygen gas. The candle that is not covered with the glass will only go out when the wax runs out. This is because there is so much oxygen gas in the environment. In the other candle, the glass limits the amount of oxygen. Once all this gas is consumed, the candle will go out. So:
Combustion - chemical reaction that always produces heat. It is a burning.
Fuel - substance that can be burned.
Oxidizer - what fuels combustion.
In the experience we have:
- heat source - lit phosphorus
- fuel - candle
- oxidizing - oxygen gas
The fuels may be solid, liquid or gaseous.
The solids can be: fabrics, paper, wax, wood.
Liquids can be: gasoline, alcohol, kerosene.
Gases can be: cooking gas, hydrogen.
Combustion is a chemical reaction that always produces heat (exothermic) in the form of energy.
The candle flame produces light (light energy) and heat (thermal energy).
The gasoline that burns in the car engine and makes it move (mechanical energy) produces heat (thermal energy).
In combustion, water vapor and carbon dioxide are also released. Some of these gases can pollute the atmosphere.
Fossil fuels are the most polluting. They are: petroleum derivatives (oil, gasoline, natural gas, kerosene) and coal. They are used in vehicles, factories and steel mills.
Combustion is fundamental and very useful for man's life. We use combustion:
- on the gas stove for preparing food;
- gasoline, alcohol, oil, kerosene in cars, airplanes;
- oil, firewood and coal in industries.
- produced by a torch to weld sheet metal.
Losses of combustion
Sometimes combustion brings harm to man and the environment. Toxic residues resulting from burning pollute the atmosphere. Fire burns cause physical defects and even the death of people. Forest and house fire is also a result of combustion.
In the candle flame there are three distinct parts, called zones or cones.
The blue zone or gas cone is the central and warmest part. It is at the base of the flame. The bright zone or yellowish light cone lies between the gas cone and the outer end of the flame. It is the brightest part due to the glow of carbon particles. The hot zone or cone of fire is the red and outermost part of the flame.