Combustion Reaction

Introduction

Aeroplanes, space rockets, and model rockets project through the atmosphere by employing concepts of mechanics. These types of machinery contain advanced propulsion systems that generate power and thrust to project the aircraft. The power inside these aircraft is generated by burning fuel or by combustion. The substance that acts as fuel combines with an oxidizer to form chemical products. These newly generated chemical substances are known as exhaust. When the exhaust is produced energy is generated in the form of heat. To start combustion a source of heat is required. Therefore, heat is not only required to initiate a combustion reaction but is also a product of combustion.

What is a Combustion Reaction?

A combustion reaction is an exothermic chemical reaction between a fuel (or reductant) and an oxidant which combines to produce oxidized products. This process takes place at high temperatures. Since this reaction involves simultaneous reduction and oxidation of substances it is a redox reaction.

For example, a struck match generates friction that raises the temperature (or energy) of the head (more than activation energy) at which the chemicals react and generate more energy in form of heat that tends to escape into the atmosphere. A moist head of matchstick or the presence of blowing wind resists the increase in temperature. Therefore, the head of the matchstick fails to burn. The burning of fuel in automobiles that generate smoke is another common example of combustion.

Examples of Combustion Reactions

Combustion of methane

Methane is a natural gas and is the cleanest fossil fuel to combust. By cleanest, it means that it does not produce any harmful toxins. It is completely broken down into water and carbon dioxide.

Combustion of butane

The combustion process to break down butane is employed in lighters. Butane is much cheaper than other fossil fuels. This is also a clean fuel but it also releases large amounts of carbon dioxide into the atmosphere.

Combustion of butanol

The process of combustion of butanol takes place in transportation. Butanol has low vapour pressure and high energy density. Therefore, it can be regarded as a biofuel. This process of combustion is used in internal combustion engines or IC engines.

Types of Combustion Reactions

There are two broad categories of combustion reactions

Complete combustion

As the name suggests, the reactant burns entirely in the presence of dioxygen and produces exhaust and products. When the compounds are ignited, the product thus formed are generally oxides of the compounds. For example, carbon will form carbon dioxide, sulphur will form sulphur dioxide, iron will form iron dioxide and so on. This type of combustion is common in industries that involve the production of fire on a large scale. In such industries air supplies the necessary amount of oxygen for the progression of the reaction.

Incomplete combustion

Occurs when there is insufficient oxygen to bring about the breakdown of fuel into oxide and water. Unlike complete combustion, the products of combustion are carbon as soot and dust, carbon monoxide; a poisonous gas and hydroxides. Incomplete combustion also takes place in a flame trap. Pyrolysis occurs before combustion in wood or coal. This can produce harmful toxic substances that are hazardous to humans and the environment. Inhaling carbon monoxide leads to loosing of consciousness and eventually death.

Why is a Combustion Reaction an Oxidation Reaction?

An oxidation reaction is a reaction in which the addition of oxygen takes place. In a combustion reaction, oxygen combines with reacting substances to form oxides. The oxides can be dioxides or monoxides depending on the type of combustion taking place. Therefore, a combustion reaction is an oxidation reaction.

Combustion Equations

Combustion of methane

$$\mathrm{CH_{4}(g)\:+\:2O_{2}(g)\:\rightarrow\:CO_{2}(g)\:+\:h_{2}O(g)(complete)}$$

$$\mathrm{4CH_{4}(g)\:+\:7O_{2}(g)\:\rightarrow\:2CO_{2}(g)\:+\:2CO(g)\:+\:8H_{2}O(l)(incomplete)}$$

Burning of naphthalene

$$\mathrm{C_{10}H_{8}(g)\:+\:12O_{2}(g)\rightarrow\:4CO_{2}(g)\:6H_{2}O}$$

Combustion of ethane

$$\mathrm{2c_{2}H_{6}(g)\:+\:7O_{2}(g)\:\rightarrow\:4CO_{2}(g)\:+\:6H_{2}O}$$

Combustion of butane

$$\mathrm{2c_{4}H_{10}(g)\:+\:13O_{2}(g)\:\rightarrow\:8CO_{2}(g)\:+\:10H_{2}O}$$

Combustion of methanol

$$\mathrm{2cH_{3}OH(g)\:+\:3O_{2}(g)\:\rightarrow\:2CO_{2}(g)\:+\:4H_{2}O}$$

Combustion of propane

$$\mathrm{2C_{3}H_{8}(g)\:+\:7O_{2}(g)\:\rightarrow\:6CO_{2}(g)\:+\:8H_{2}O}(complete)$$

$$\mathrm{2C_{3}H_{8}(g)\:+\:9O_{2}(g)\:\rightarrow\:4CO_{2}(g)\:+\:2CO(g)\:+\:8H_{2}O}(incomplete)$$

How is Combustion different from Burning?

Burning	Combustion
The process of setting material or substances on fire.	The process of combination of a fuel with the oxygen or oxidant.
It results in the formation of a flame. A blue flame is formed during complete combustion and a yellow-orange flame is formed during incomplete combustion.	It may or may not ignite a flame. A blue flame is formed during complete combustion and a yellow-orange flame is formed during incomplete combustion.
A relatively low amount of energy is liberated.	A relatively high amount of energy is liberated.
Light is always produced along with heat energy.	Light may or may not be produced along with heat energy.
The products formed in burning are carbon dioxide, carbon monoxide, solid carbon as soot and water as vapours.	The products depend on the type of combustion taking place. In complete combustion, carbon dioxide and water are formed. In incomplete combustion, carbon monoxide and carbon are formed.
It is a type of combustion.	It is broadly categorized into complete and incomplete combustion.
It requires a flammable material along with reacting substances.	It may or may not require a flammable material along with a reacting substance.
It generally takes place in solid fuels	It generally takes place in hydrocarbons.

Applications of the Combustion Reaction

There are numerous applications of combustion reactions −

• Combustion reactions are used in gas grills, gas stoves, cookwares, fireplaces etc.

• Methanol undergoes combustion to produce wood alcohol

• Butane undergoes combustion inside domestic lighters.

• In metallurgical industries, combustion is employed to generate steam.

• Combustion is used in explosives.

• Combustion is employed in internal combustion engines.

• Rocket propulsion also involves the combustion of fuels.

• Combustion is used in engines of all automobile vehicles.

Harmful Effects of Combustion

There are many harmful effects of both incomplete and complete combustion −

• Carbon is produced in incomplete combustion as soot. Soot is harmful to humans and can cause asthma and other severe breathing issues. It can even cause cancer.

• Carbon monoxide produced in incomplete combustion when enters the respiratory system can combine with haemoglobin in the place of oxygen.

• Carbon monoxide and carbon dioxide can combine with water and oxygen present in the atmosphere and produce acid rain. This acid rain is made up of sulphuric and nitric acid and harms the biosphere of an area.

• Carbon monoxide when reached inside the human body can cause vomiting, headache and nausea.

• An excessive amount of carbon dioxide produced during combustion can have adverse effects on human health.

• Carbon dioxide is one of the greenhouse gas and contributes to global warming.

Conclusion

Combustion is an important and useful process for human society. From gas stoves and automobiles used in households to large-scale industries and rocket propulsions, combustion reactions are the working force behind many principal processes. Although combustion reactions are fundamental, they have many disadvantages. A large number of harmful byproducts are formed in combustion reactions. These by-products are toxic to humans and the environment. combustion reactions are not very environmentally- friendly reactions. Combustion reactions generally involve the burning of fossil fuels which are non-renewable resources. Therefore, combustion must be done in a controlled manner to prevent the extinction of valuable fossil fuels.

FAQs

1. What is the balanced equation for the incomplete combustion of nonane?

$$\mathrm{C_{9}H_{20}(l)\:+\:\frac{27}{7}O_{2}(g)\:\rightarrow\:8CO_{2}(g)\:+\:CO(g)+\:10H_{2}O}(l)$$

$$\mathrm{C_{9}H_{20}(l)\:+\:13O_{2}(g)\:\rightarrow\:8CO_{2}(g)\:+\:C(g)+\:10H_{2}O}(l)$$

$$\mathrm{C_{9}H_{20}(l)\:+\:\frac{27}{7}O_{2}(g)\:\rightarrow\:7CO_{2}(g)\:+\:CO(g)+\:+\:C(S)\:+\:10H_{2}O}(l)$$

2. What are biofuels?

The fuel derived from biomass is known as biofuel. It can be solid, liquid or gas. For Example–the formation of bioethanol from charcoal, sugar cane or corn or the production of biogas by decomposing waste via anaerobic respiration.

3. What are combustible substances?

The substances that are easily flammable and undergo combustion are called combustible substances. For Example – LPG, CNG, wood, paper, clothes, etc.

4. What are non-combustible substances?

The substances that do not ignite easily or undergo combustion even on reaching appropriate temperatures are called combustible substances. For example – brick, concrete, glass, etc.

5. What is an ideal fuel?

An ideal fuel is a fuel that on combustion does not produce harmful gases like carbon monoxide or toxic residual substances such as carbon. It should have high calorific value and should be cheap, conveniently accessible, transportable and readily combustible.