What are Combustion Reactions?

Combustion is the oldest technology of mankind and can be regarded as one of our most important discoveries or inventions. It has a very long history. From ancient times to the Middle Ages, fire was considered one of the four basic elements of the universe, along with Earth, water, and air. Combustion, explosions, and flames have been observed and assumed since the early days. Every culture has its own reasons. The Greeks interpreted burning in terms of philosophical teaching. One is that every fuel assembly has a clear “flammable principle” that escapes when the body burns and reacts with air. Fire has long been used by humans for a variety of purposes, including cooking, metalworking, and war. However, due to the complexity of combustion phenomena, significant advances in understanding combustion theory have only been achieved in the last few decades through close cooperation between experimenters and theories.

Combustion is a chemical process or reaction between a fuel (hydrocarbon) and oxygen. When fuel and oxygen react, heat and light energy is released. Then heat and light energy is generated in the flame. Therefore, the formula for the combustion reaction is hydrocarbon + oxygen = thermal energy. Combustion is used in automobile engines, rocket engines, and many other machines. 

Different types of combustion

There are five different types of combustion that are explained below

Complete Combustion: Complete combustion occurs with an unlimited supply of air, especially oxygen. Complete combustion is also called clean combustion. Here, the hydrocarbon burns completely with oxygen, leaving only two by-products, water, and carbon dioxide.   This example is when the candle is burning. The heat from the core evaporates the wax, which reacts with the oxygen in the air. The two reaction products are water and carbon dioxide. Ideally, all wax will burn out and burn completely.

CH₄ + 2O₂    ⇢    CO₂+ 2H₂O+ energy

Incomplete Combustion: Incomplete combustion occurs when the air supply is restricted. And, in contrast, complete combustion, is also known as dirty combustion. Due to a lack of oxygen, the fuel will not react completely. Instead of carbon dioxide, carbon monoxide and soot are produced.  An example is the burning of paper. It leaves ash (a type of soot) as a by-product. Incomplete combustion, the only products are water and carbon dioxide. Also, incomplete combustion produces less energy than complete combustion.

4CH₄ + 5O₂    ⇢    2CO+ 8H₂O  + 2C

Rapid Combustion: Another type of burn is rapid combustion. Fast energy requires external thermal energy to facilitate the reaction. Combustion produces a large amount of heat and light energy, which is done very quickly. Combustion will continue as long as fuel is available.

An example is when you light a candle. When you light a candle with a match, it provides heat energy. And that continues until the wax burns out. Therefore, it is rapid combustion.

Spontaneous Combustion: As the name implies, this combustion is Spontaneous. This means that no external energy is required to initiate combustion. This is caused by self-heating. Substances with a low ignition temperature are heated and this heat cannot be dissipated. The reaction for pyrite in presence of air.

2FeS₂   +  11/2 O₂    ⇢  Fe₂O₃  +  4SO₂

The temperature rises above the ignition point and combustion occur when there is sufficient oxygen. One example is the reaction between alkali metals and water.

Explosive Combustion: Explosive combustion occurs when the reaction occurs very quickly. The reaction occurs when something ignites and produces heat, light, and sound energy. The easiest way to explain it is to call it an explosion.

The explosion of ammonium nitrate

NH₄NO₃    ⇢  2H₂O +  N₂  + ½ O₂

Combustion Reaction as an Oxidation Reaction

Combustion reactions cannot occur without oxygen. In order for combustion or combustion to occur, oxygen must be present, as it is the only gas that supports combustion. Whenever a substance reacts with oxygen to release energy, a combustion reaction occurs. For example, when methane burns in oxygen, it releases carbon dioxide and water. The formation of carbon dioxide indicates that the carbon present in methane has been oxidized.

CH₄ + 2O₂    ⇢    CO₂+ 2H₂O+ energy

Examples of Combustion

• Combustion of sulfur in the air.

S + O₂    ⇢   SO₂

•   An explosion of hydrogen in the air.

H₂  +  O₂   ⇢ H₂O  +  Energy

• Combustion of naphthalene.

C₁₀H₈ + 12O₂    ⇢    10CO₂ + 4H₂O.

•   Combustion of propane i.e, grills, fireplace, etc.

2C₃H₈ + 7O₂ → 6CO₂ + 8H₂O

Difference between combustion and burning

Combustion	Burning
It is just a chemical reaction	It is a  physical phenomenon that sets a fire to some object
It may or may not produce sparks	It produces sparks
It produces a large amount of heat	It produces less amount of heat
light energy is produce	It may or may not produce light energy

Harmful effects of combustion

During combustion, the chemical energy stored in the fuel is converted into heat and light. Incineration is used for the propulsion of locomotives, vehicles, industrial machinery, and many other uses. Smoke from combustion pollutes the atmosphere. Every day the number of industries is increasing. As a result, the continuous burning of fuel and the release of smoke from chimneys and automobile exhausts increase the amount of carbon dioxide in the atmosphere, destroying its original composition. 
The main products that are formed during fuel combustion and have a harmful effect are Carbon fuels such as wood, coal, and oil release unburned carbon particles. These fine particles are dangerous pollutants that cause respiratory problems like asthma.

Sample Questions

Question 1: Why is combustion so important? 

Answer:

The combustion reaction is a very important class of chemical reactions. Such answers are essential to our daily lives. The combustion reaction occurs when fuel and oxygen react to produce fire or heat and light. Combustion occurs when gasoline (usually fossil fuel) reacts with oxygen in the air to generate heat. The heat generated by the burning of fossil fuels is used to power machines such as boilers, stoves, ovens, and motors.

Question 2: What kind of reaction is combustion? 

Answer:

The combustion reaction is a reaction in which a substance reacts with oxygen gas in the form of light and heat to release energy. The combustion reaction must contain O₂ as a reactant. When hydrogen gas burns, water vapor is generated.

Question 3: What is the cause of combustion?

Answer:

Spontaneous combustion can occur when materials with relatively low ignition temperatures (hay, straw, peat, etc.) begin to release heat. Combustion occurs when sufficient oxidizers and fuels, such as oxygen, are available to sustain the thermal runaway reaction.

Question 4: Can it burn without oxygen?
Answer:

Incomplete combustion occurs when a reaction to combustion occurs without proper oxygenation. Incomplete combustion is undesirable because it absorbs less energy than complete combustion and produces a toxic gas called carbon monoxide.

Question 5: What is the need to use combustion? 

Answer: 

Burning fossil fuels such as coal and petroleum, or thermal energy from renewable fuels such as firewood, is recovered for a variety of applications such as cooking, power generation, and industrial or household heating. Combustion is also the only process actually used to fuel rockets.