What is Combustion?
Combustion refers to the process where a substance burns in the presence of Oxygen, giving off heat and light in the process.
You might have heard that certain substances are combustible whereas some are non-combustible. Combustible substances are simply those that undergo this process.
But isn’t Oxygen the most abundant substance on Earth? Doesn’t it combine with most of the elements? But surely, not all reactions can be said to be similar to this process. Even many people believe rusting of Iron is a similar process as rusting involves iron combining with oxygen giving off heat.
So what differentiates combustion from similar processes? It is the spontaneity with which substances react with Oxygen which defines a reaction.
Hydrocarbon + Oxygen → Carbon Dioxide + Water + Heat Energy
When fuel, most typically a fossil fuel, combines with oxygen in the air to generate heat, combustion occurs. The heat produced by the combustion of a fossil fuel is utilised to power boilers, furnaces, kilns, and motors.
History Of Combustion
Combustion can be considered the oldest technology of mankind, and one of our most important discoveries or inventions. Combustion has a very long history. From antiquity up to the Middle Ages, fire along with earth, water, and air was considered to be one of the four basic elements in the universe. Combustion, explosion, and flame have been witnessed and hypothesized from the earliest ages. Each culture has its own reason for it. The Greeks interpreted combustion in terms of philosophic doctrines, one of which was that there was a certain “inflammable principle” in all fuel bodies, and that principle escaped when the body was burned to react with air.
Fire has been used by man for a long time for various purposes, such as cooking, metal production and warfare. However, as combustion phenomena are complex, significant advances in the understanding of combustion theory were only made in the last decades by a close collaboration between experimentation and theoreticians.
Examples of Combustion
When substances react spontaneously with Oxygen giving off heat and light, the heat released fuels the process further making the reaction violent and rapid. If nothing is done to control this process, it takes the shape of a fire. It is this spontaneous and violent nature that distinguishes combustion from other similar processes taking place in the presence of Oxygen.
Some examples of combustion are
- Burning of sulfur in the air
- An explosion of hydrogen in air
- Burning of Wax candle
- Combustion of petrol in a car’s engine
- Burning of natural gas in a bunsen burner
- A bush fire means wood cellulose and other fuels burn in oxygen
The burning of methane, the main ingredient of natural gas, is an example of a normal reaction to burning. Stoves and furnaces operating on natural gas have a pilot light or a spark to provide the initial energy required to trigger the combustion reaction.
Magnesium burning does not emit carbon dioxide or water vapor, but it is also a combustion process since it is an exothermic reaction of a fuel substance with oxygen. Placing magnesium in the air is not enough to start burning, but a spark or flame splits the bonds between oxygen molecules in the air to allow the reaction to continue.
Special Combustion Reactions
Flames are undoubtedly the medium first used in which atomic collision processes play an important role. Knowledge of elementary combustion reactions continues to be essential for developing more economical methods for use of fossil-fuel supplies. The term “flame” in its broadest sense includes any luminescent reaction process and combustion any relatively fast gas phase reaction.
Hydrogen combustion induces complex chain reactions involving the collision of nitrogen and oxygen atoms with oxygen and hydrogen molecules, respectively, to create hydroxyl radicals. The final reaction product is gas, formed by a mixture of hydroxyl and hydrogen molecules.
In order to continue with the combustion reaction, fuel materials and oxygen must be present as well as an external source of energy to initiate the combustion cycle. Although certain material will spontaneously burst into flame when mixed with oxygen gas, most substances require a spark or other form of energy to start burning. If the combustion reaction begins, the heat produced by the reaction is adequate to continue
Types of Combustion
Let us now study the types of such reactions.
- Complete combustion: When the reaction takes place in the presence of abundant Oxygen, the substances combine with Oxygen to their maximum extent. Such reactions have heat and light as a visible by-product.
- Incomplete combustion: These are defined as the reactions that occur in the absence of sufficient oxygen because of which substances are unable to burn completely. Such reactions leave Soot in the container due to this process along with the formation of Carbon monoxide which is an air pollutant.
Apart from classifications based on the availability of Oxygen, reactions are also categorized based on their spontaneity and rate of reaction. Reactions that proceed violently can either lead to fire or even explosion (which is also accompanied by loud noise). Formation of rust can also be categorized under slow combustion.
Frequently Asked Questions – FAQs
What is combustion in chemistry?
Combustion is the scientific word that burns. During a combustion reaction, the material reacts with oxygen from the air and contributes energy to the atmosphere as light and heat. The products of the reaction to combustion are called oxides.
What is Combustion example?
Combustion reactions occur as oxygen reacts with another element and emits heat and light. The burning of sulphur, natural gas, and sparklers are also typical forms of combustion reactions. Essentially, any reaction that involves burning it is a reaction of combustion.
How do we use combustion?
Thermal energy derived from the combustion of either fossil fuels such as coal or oil or from renewable fuels such as firewood is extracted for a range of uses, such as cooking, power generation or industrial or domestic heating. Combustion is also the only process actually used to fuel rockets.
What are some examples of spontaneous combustion?
The burning of a material or object by the accelerated oxidation of its own materials without heat from any external source is known as spontaneous combustion. Example: Phosphorous and sulphur continue to burn instantaneously; at room temperature.
What type of reaction is combustion?
The process of combustion is a process in which the material reacts with oxygen dioxide, releasing energy in the form of light and heat. Combustion reactions must require O2 as a single reactant. Hydrogen gas combustion produces hydrogen vapour. Remember that this reaction is often described as a mixture reaction.
Why is combustion so important?
Combustion reactions are a very important class of chemical reactions. Such responses are vital to our daily lives. The combustion reaction happens as the fuel and oxygen react, creating fire or heat and light. Combustion happens as the gasoline, most commonly a fossil fuel, reacts with the oxygen in the air to create heat. The heat produced by the combustion of fossil fuels is used in the operation of machinery such as boilers, furnaces, ovens and engines.
What type of reaction is combustion?
A combustion reaction is a reaction in which a material, in the form of light and heat, reacts with oxygen gas, releasing energy. As one reactant, combustion reactions must include O2. Hydrogen gas combustion produces water vapour.
What causes combustion?
When a material with a relatively low ignition temperature (hay, straw, peat, etc.) starts emitting heat, spontaneous combustion may occur. Combustion occurs if there is sufficiently oxidizer, such as oxygen, and fuel available to sustain the thermal runaway reaction.
Is combustion possible without oxygen?
Incomplete combustion happens where a reaction to the combustion happens without adequate oxygen supply. Incomplete combustion is also unwanted because it absorbs less energy than complete combustion and creates a toxic gas called carbon monoxide.
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