Combustion of Hydrocarbons Alkanes

Introduction

Hydrocarbons as the name suggests are a combination of hydrogen and carbon molecules. Combustion refers to the process where a substance burns in the presence of oxygen, or, the substance undergoes burning in the presence of air or oxygen to give heat and light. Combustion of hydrocarbons refers to the chemical reaction where hydrocarbons(alkanes or alkenes) react with oxygen to create or give carbon dioxide, water, and a large amount of heat energy. Combustion is a kind of exothermic reaction. These hydrocarbons are used for the formation of primary constituents of fossil fuels, like petroleum, coal, natural gas, e.t.c. One of the important things which I would like to mention here is that CO₂ will always get produced or released in the hydrocarbon combustion or hydrocarbon reaction, and it doesn’t matter what type of hydrocarbon molecule we are taking.

Combustion of alkanes

Alkanes are those compounds having the chemical formula [C_n H_2n+2]. Some of the commonly used or mostly known alkanes are methane and ethane. Combustion of hydrocarbons (alkanes here) depends on the amount of oxygen supplied or available. So, depending upon the amount of oxygen supplied, the combustion of alkanes can be divided into two major categories that are complete combustion and incomplete combustion.

Complete Combustion of Alkanes

Complete combustion of alkanes takes place or occurs when there is a continuous or plentiful amount of oxygen available. Then the carbon and hydrogen atoms present in the alkane easily react with the oxygen molecules and lead to an exothermic reaction. An exothermic reaction is defined as a chemical reaction that involves the release of energy or generates energy either in the form of heat or light. Here, the reactants will break down to form products along with the release of energy.

Yulo1985, Methane-combustion, CC BY-SA 4.0

• Here the products formed will be carbon dioxide (CO₂) and water molecules.

• A larger amount of energy will be thrown out during the reaction.

• $$\mathrm{Example- Ethane(C_2 H_6 )_ + oxygen(O_2 )→ carbon dioxide(CO_2) + water(H_2O).}$$

Incomplete Combustion of Alkanes

Incomplete combustion of alkanes takes place or occurs when there is a very less or limited amount of oxygen available. Then the carbon and hydrogen atoms present in the alkane hardly or rarely manage to react with the oxygen molecules.

James Riden <jamesr@europe.com>, Gas cooker blue flame, CC BY-SA 2.5

• Here the products formed will be carbon monoxide, carbon (soot) and water molecules.

• Less amount of energy will be released as compared to complete combustion.

• Example- Burning of coal, paper, wood, e.t.c.

Combustion of Hydrocarbons (Alkene)

Alkenes are those compounds having the chemical formula [C_n H_2n]. Some of the commonly used or mostly known alkenes are ethene, propene, and butene. Combustion of hydrocarbons (alkenes here) is very less likely to occur as compared to alkanes. Again, here also the combustion will depend upon the amount of oxygen supplied. And based on the amount of oxygen supplied it is further divided into two parts that are complete combustion and incomplete combustion.

Complete Combustion of Alkene

Complete combustion of alkenes takes place or occurs when there is a continuous or plentiful amount of oxygen available. Then the carbon and hydrogen atoms present in the alkene easily react with the oxygen and lead to an exothermic reaction.

• Here, also the products formed are carbon dioxide and water molecules.

• A large amount of energy will be released here.

Combustion of Hydrocarbons

Hydrocarbons are made up of hydrogen and carbon molecules. Combustion refers to the process in which the substance burns or reacts in the presence of oxygen. So, hydrocarbon combustion is the chemical reaction where hydrocarbons like alkane and alkenes react with the oxygen or atmospheric air to liberate or produce carbon dioxide, water and heat. Combustion of hydrocarbons releases a large amount of energy because it is an exothermic reaction by nature and thus it acts as a primary or most important constituent for the formation of fossil fuels like natural gas. Now, it is further classified into two major categories based on the amount of oxygen supplied to them. And those categories are- Complete combustion of Hydrocarbons and Incomplete Combustion of Hydrocarbons.

Complete Combustion of Hydrocarbons

Complete combustion of hydrocarbons takes place or occurs when there is a plentiful or good supply of oxygen or air. And, the carbon and hydrogen atoms of the hydrocarbon will react with the oxygen to release a large amount of energy thus the reaction is called an exothermic reaction.

• Here, the products formed are generally carbon dioxide and water.

• As it is an exothermic reaction, a large amount of energy in the form of heat will be given out.

Incomplete Combustion of Hydrocarbons

Incomplete combustion of hydrocarbons takes place or occurs when there is a limited or poor supply of oxygen or air. And, the carbon and hydrogen atoms of the hydrocarbon will hardly or rarely react with the oxygen to release less amount of energy as compared to the complete combustion of hydrocarbons.

• Here the products formed are carbon monoxide, water, and carbon (soot).

• A very less amount of energy is released here as compared to complete combustion.

Trends in Combustion

• The burning of hydrocarbons depends or varies inversely with the molecular weight of the hydrocarbons.

• Increasing molecular weights create difficulties in the burning of hydrocarbons and vice-versa.

• So, for a hydrocarbon, if complete ignition occurs then it burns with a bluish flame.

• And, if the molecular mass of the hydrocarbon increases then, it starts burning with a yellowish flame showing incomplete combustion.

Conclusion

Hydrocarbons are the combination of hydrogen and carbon molecules and combustion is the process in which the substance burns or reacts in the presence of oxygen to produce heat and light energy. Further, the Combustion of Hydrocarbons takes place when the hydrocarbons or alkanes or alkenes react with the oxygen or air to liberate water and carbon dioxide. But further, the combustion of hydrocarbons depends on the amount of oxygen supplied to the substance. If the oxygen supply is in more than the required amounts then, complete combustion will take place but if the oxygen supply is limited or controlled then the incomplete combustion will take place and the products formed in both the cases will be quite different.

FAQs

1. What are hydrocarbons?

Hydrocarbons are organic compounds entirely composed of hydrogen and carbon atoms. These are the examples of group 14 hydrides. Here, the carbon atoms join together to form the skeleton or framework of the compound, and the hydrogen atoms attach to them in many different configurations.

2. Define combustion.

Combustion is defined as a chemical process or chemical reaction, where a substance burns or reacts with the oxygen or air(mainly oxygen) present in the air to give energy in the form of heat and light.

3. What do you mean by complete combustion?

Complete combustion means when combustion occurs in an unlimited or plentiful supply of oxygen or air. Here the products formed are mostly carbon dioxide and water.

4. What are the products formed from the incomplete combustion of an alkane?

The products formed from the incomplete combustion of an alkane are carbon monoxide, Carbon (soot), and water. Among these, carbon monoxide is one of the major air pollutants which is very harmful to the living creatures on this planet.

5. Define Carbon (soot).

Soot is defined as a mass of impure carbon particles formed or produced due to incomplete combustion of the hydrocarbons. Major sources of soot are burning coal, wood, and oil used in industries and forest fires.