Combustion of Hydrocarbons

Combustion Of Hydrocarbons Alkanes

Combustion is a process of burning some substances at high-temperature. It is an exothermic reaction which happens between fuel and oxygen, producing a gaseous substance (smoke) as a product. Combustion is of two types, one is complete combustion and another is incomplete combustion. 

Whereas, the Hydrocarbons are compounds made only with the elements of hydrogen and carbon. Hydrocarbons are broadly classified as alkanes, alkenes, and alkynes.


Complete Combustion Of Alkanes

It is the process of burning the alkane in the presence of sufficient air or oxygen, it produces carbon dioxide, water, and a huge amount of heat as a product. For example:

  1. With Propane ( C3H8 ), the Complete Reaction is Given as Follows,

C3H8 + O2  → 3CO2 + 4H2 

  1.  With Butane (C4H10), the Complete Combustion Reaction is Given as Follows,

C4H10 + O2  → 4CO2 + 5H2 

The generalized form of this reaction as follows:

CnH2n+2 + ((3n+1)/2) O2   →  nCO2 + (n+1) H2

In general, it is used as a fuel since it produces a huge amount of heat.


Incomplete Combustion Of Alkanes

It is the process of burning the alkane in the absence of sufficient air or oxygen. It produces carbon and carbon monoxide as a product whereas carbon monoxide is a by-product which is a colourless poisonous gas. For example:

With methane (CH4), the incomplete reaction is given as follows:

CH4 + O2  → C + 2H2O

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The carbon black which is formed as a product of the combustion process is used in the manufacturing of inks. 


Combustion Of Hydrocarbons(Alkene)

Complete Combustion of Alkene

Like the same as an alkane, alkene also undergoes complete combustion. It occurs in the presence of excess air or oxygen for combustion. For example:

CH2 + 3O2    →  2CO2 + 2H2

Incomplete Combustion of Alkene

It happens in the absence of oxygen during the combustion process and carbon monoxide is formed as a product instead of carbon dioxide. For example:

CH2 + 2O2     →  2CO + 2H2


Combustion Of Hydrocarbons  

It is the process of burning the hydrocarbons which lead to break the bonds either in the presence or in the absence of excess oxygen.

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Complete Combustion of Hydrocarbons

It is the process of burning of hydrocarbons in excess of oxygen and yields carbon dioxide and water as a product. Oxygen should be present excess and hydrocarbon is used as a limiting reagent to achieve this process. 

Incomplete Combustion of Hydrocarbons

It is a process of burning hydrocarbons in the absence of excess oxygen and produces the most oxidized form of carbon which is carbon dioxide as a product. We should have oxygen as a limiting reagent and hydrocarbons as an excess reagent.

The “sooty” flame is produced by the incomplete combustion of a hydrocarbon, due to the presence of carbon ( C ). 

Hydrocarbon Formula of Complete Combustion

The general form of this combustion reaction is as follows:
Methane  +  oxygen gas  →  carbon dioxide gas + water vapour

Hydrocarbon Formula of Incomplete Combustion
The general form of this incomplete reaction is given as follows:

methane  +  oxygen gas  →  solid carbon  +  water vapour


Solved Examples

  1. Ethanol is a fuel source in an alcohol lamp. The formula for ethanol is given by

         C2H5OH. Write the balanced equation for the process of combustion of ethanol.

Solution:

Step 1: Think of the given problem 

The question is given on ethanol which is a reactant and also with oxygen. Carbon dioxide and water are the product.

Step 2: Write the skeleton equation and solve:

C2H5OH(l) + O2(g) → CO2(g) + H2O(g)

Now balance the equation.

C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)

Evaluate the number of each element present on the reactant and product side.


Interesting Facts:

Nearly 21% of the air in the atmosphere is filled with oxygen. To get complete combustion, it is necessary to have plenty of air, mainly oxygen in it. Natural gas and petrol are such fuels that have hydrocarbons.

A hydrocarbon is a compound made of only 2 elements namely carbon and hydrogen atoms.

The interesting thing is, it is found in crude oil and can be separated by fractional distillation. The bond between them is non-polar covalent bonds.

FAQ (Frequently Asked Questions)

1. What are the Products of Combustion of the Hydrocarbon?

In the presence of an excess of air, complete combustion of a hydrocarbon produces carbon dioxide and water as products In further.

In order to achieve the complete combustion of hydrocarbon, oxygen should be in excess and hydrocarbon is treated as limiting reagents.

 For example: 

C3H8 + O2  → 3CO2 + 4H2 

The above equation shows us, in excess of oxygen the carbon dioxide is formed as a product.

While in case of incomplete combustion, it produces carbon monoxide,  water and carbon as a product.

In order to achieve this reaction, oxygen is used as limiting reagents and hydrocarbon is used in excess.

For example:

CH2 + 2O2     →  2CO + 2H2O

The above equation shows us, in the absence or insufficient of oxygen it forms carbon monoxide as a product.

2. What are the Broad Classifications of the Hydrocarbon?

The hydrocarbon is broadly classified as Alkanes, alkenes, and alkynes. Let's see in brief about the classifications.

  • Alkanes are saturated hydrocarbons means, they formed by a single bond in between the carbon atoms. The general representation of alkane is CnH2n+2 in case of non-cyclic structures. There are four bonds for each carbon atom in alkane, C- H or C- C bond are possible one. Alkane type is not very reactive due to the stability of the carbon bond.

  •  Alkenes are unsaturated hydrocarbons means, they are formed by one or more double bonds in between the carbon atoms. The general representation of alkene is CnH2n. Alkenes are more reactive when compared with alkanes, this is due to the presence of pi bond ruptures in it. 

Alkynes are also unsaturated hydrocarbon carbons like same as alkenes. Alkynes are made by one or more triple bonds in between the carbon atoms. The general representation of alkyne is CnH2n-2. Alkynes are considered as more reactive than the alkenes and alkanes. They are highly reactive due to the availability of triple bonds and able to undergoes addition reactions more readily.