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Oxidation
by Ron Kurtus (2 April 2007)
Oxidation is the chemical combination of oxygen and another element or molecule. There are many common examples of oxidation, including the burning of carbon-based fuels.
This oxidation process can be rapid, where a material burns, or it can be slow, where a material gradually oxidates over time.
Questions you may have include:
- What are some examples of oxidation?
- What is rapid oxidation?
- What are some forms of slow oxidation?
This lesson will answer those questions.
Examples of oxidation
Oxidation is the chemical combination of oxygen with another substance. A few examples of oxidation include:
Sulfur plus oxygen yields sulfur dioxide: S + O2 → SO2
Carbon plus oxygen yields carbon dioxide: C + O2 → CO2
Magnesium plus oxygen yields magnesium oxide: 2Mg + O2 → 2MgO
Iron plus oxygen yields iron oxide (rust): 3Fe + 2O2 → Fe3O2
Phosphorus plus oxygen yields phosphorus pentoxide: 4P + 5O2 → 2P2O5
(Note how the number of each element on the left of the chemical equation equals those on the right side.)
Rapid oxidation
Rapid oxidation results in burning of a material or even an explosion. It happens rapidly and produces light and noticeable heat.
Combustion or burning is rapid oxidation. But combustion can also refer to rapid burning where oxygen is not involved. An explosion is when the combustion is extremely rapid and results in outward forces from the point of oxidation.
Often heat is required to initiate rapid oxidation. The kindling temperature is what is required to start the burning process.
Slow oxidation
Slow oxidation occurs so slowly at ordinary temperature that it produces no light and no noticeable heat. The rusting of iron and the rotting of wood are good examples of slow oxidation.
Difficult to detect heat
It is difficult to detect the heat given off when slow oxidation takes place, because it escapes gradually into the surroundings. Careful measurements show that the amount of heat given off is what would be predicted in a rapid oxidation of the material.
Spontaneous combustion
Spontaneous combustion is a case when slow oxidation takes place, but the heat is not permitted to escape. It gradually it accumulates until the kindling temperature is reached, and which time the material may start burning.
One example of this is seen when piles of hay in a farmer's field become wet and the hay starts to rot inside the pile. Sometimes the temperature inside can become great enough to start the pile of hay on fire.
Summary
Oxidation is the chemical combination of oxygen and another substance. One of many examples of oxidation is the combination of carbon and oxygen, resulting in carbon dioxide. There are two major types of oxidation: rapid oxidation and slow oxidation.
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