Combustion
D. Crowley, 2007
Monday, July 31, 2017
Combustion
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To be able to explain combustion
Burning Natural Gas
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Look at the burning natural gas worksheet
Answer the questions, using the diagram below for help…
Methane in low oxygen
In low oxygen two chemical
reactions take place: -
Methane in high oxygen
In normal air (high oxygen) one
chemical reactions takes place: -
methane + oxygen  carbon monoxide + water
methane + oxygen  carbon dioxide + water
2CH4 + 3O2  2CO + 4H2O
CH4 + 2O2  CO2 + 2H2O
methane + oxygen  carbon + water
CH4 + O2  C + 2H2O
Burning Natural Gas
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Carbon (soot) builds up in your chimney
The toxic gas carbon monoxide is produced
Less energy is released, as not enough oxygen reaches your burner
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Carbon monoxide can become deadly if you are subjected to
high levels of it! Also, soot can cause respiratory problems
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It will produce more energy and these waste substances, carbon
dioxide and water
Heating
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Look at the demo of heating two beakers of water
One is heated using the safety flame (yellow) and the other is
heated using the fierce flame (blue)
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What difference is there?
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Combustion
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Combustion is the chemical reaction which takes place when a
substance burns
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The substance reacts with oxygen, releasing energy (heat and
light)
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Combustion is extremely important (>90% of the world’s energy
comes from combustion reactions (e.g. fossil fuels such as coal,
natural gas and petrol)
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What is needed for combustion to take place?
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Heat
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Fuel
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Oxygen
Combustion
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Combustion is exothermic - heat is released to the surroundings
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This can also be called an oxidation reaction, as it involves oxygen
being added to the fuel
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The fuel you use will result in different combustion reactions taking
place…
Fuel
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Coal is mostly carbon - when coal burns it turns limewater cloudy
(meaning the gas produced is carbon dioxide)
carbon + oxygen  carbon dioxide
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Many other fuels are hydrocarbons - made up of hydrogen and
carbon. When they burn they produce carbon dioxide and water
methane + oxygen  carbon dioxide + water
Demo
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Watch the demo of complete combustion
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Methane is our fuel: methane + oxygen  carbon dioxide + water
CH4 + 2O2  CO2 + 2H2O
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What is the test for carbon dioxide produced?
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What is the test for the water produced?
Not Always Perfect
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A good supply of oxygen is needed for a fuel to burn completely and
release as much energy as possible
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If there is a plentiful supply of oxygen we get complete combustion
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However, if there is not enough oxygen then the fuel will not burn
completely, wasting both the fuel and reducing the energy released
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If there is not enough oxygen we get incomplete combustion
Complete combustion
Incomplete combustion
carbon + oxygen  carbon dioxide
carbon + oxygen  carbon monoxide