Combustion
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What is combustion?
Combustion is a rapid reaction between
a substance and oxygen that releases
heat and light energy. When a substance
burns, it is said to combust.
A fuel is a substance that reacts with
oxygen (combusts) to release
useful energy. Hydrocarbons, such
as those found in crude oil, make
good fuels, particularly if the
molecules in the compound are small.
A hydrocarbon is a compound containing
only the elements hydrogen and carbon.
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The products of combustion
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Oxidation and reduction
During the combustion of a hydrocarbon fuel, the carbon
and the hydrogen are oxidized.
A reaction where oxygen is added to an element is known
as oxidation. For example:
carbon + oxygen carbon dioxide
The opposite process, where oxygen is removed from a
compound is known as reduction. For example:
copper oxide + hydrogen copper + water
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Complete combustion
Complete combustion occurs when there is
enough oxygen available for all of the carbon
atoms in the fuel to burn and form carbon dioxide.
The blue flame of a Bunsen burner is an
example of complete combustion of a
hydrocarbon (in this case, almost pure
methane), where heat energy is given out.
What are the products of the complete
combustion of a hydrocarbon?
carbon
hydrocarbon + oxygen
dioxide
+ water
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Complete combustion of methane
Methane is a hydrocarbon found in natural gas. Methane will
combust in oxygen to produce carbon dioxide and water.
carbon
methane + oxygen dioxide
+ water
CH4 + 2O2 CO2 + 2H2O
Propane is a hydrocarbon fuel with the formula C3H8.
What is the balanced symbol equation for the complete
combustion of propane?
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Combustion equations
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Fuels and the environment
Most fuels contain hydrogen and carbon, but many also
contain some sulfur. When a fuel burns, several substances
may be released into the Earth’s atmosphere, including:
carbon dioxide (CO2)
water vapour (H2O)
carbon monoxide (CO)
sulfur dioxide (SO2)
oxides of nitrogen (NO)
particulates.
The conservation of atoms during chemical reactions means
that any impurities in the fuel will also end up as a product.
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Burning fuels in oxygen
Fuels burn more rapidly in pure oxygen than they do in air.
Oxygen gas can be obtained from the Earth’s atmosphere.
In welding, a fuel such as
propane is mixed with
oxygen gas allowing
temperatures of up to
3500 °C to be achieved.
At these temperatures,
metal becomes molten.
In rocket engines, the fuel is mixed with oxygen before
combustion, which allows the fuel to burn more rapidly
and achieve the power needed to blast off.
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True or false?
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Glossary
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Multiple-choice quiz
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