Combustion Reaction

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What is a Combustion Reaction?

A combustion reaction is usually a reaction that produces fire. Combustion takes place at an elevated temperature. It is a heat releasing (exothermic), redox chemical reaction that usually occurs between a fuel and oxidizing agent (mostly oxygen of the atmosphere). The products released are often gaseous, and the resultant mixture is commonly called smoke. The products of combustion are called oxides.

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Oxygen is the main ingredient for the process of combustion to take place. Combustion cannot happen in the absence of oxygen. If you leave a can of gasoline open in the atmosphere (containing oxygen), why does it not start burning?

This happens because, in order to initiate a reaction, we have to overcome its activation energy. This is done by heating the fuel so that it reaches its ignition temperature after which the combustion proceeds smoothly in the sufficient supply of oxygen.

Types of Combustion Reactions

1. Complete Combustion: Complete combustion takes place when a fuel burns completely to produce carbon dioxide and heat with a sufficient supply of oxygen. 

2. Incomplete Combustion: In the case of a limited or partial supply of oxygen, the fuel burns incompletely, thereby producing carbon monoxide in place of carbon dioxide.

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Examples of Combustion Reactions

  • Our vehicles such as cars, bikes, etc. run on fossil fuels. These fuels undergo a combustion reaction with oxygen to run the engine. 

  • Burning of wood or other solid fuels such as coal in winters: The carbon content present in wood or coal reacts with oxygen of the atmosphere to release heat and form other gaseous products.

  • The liquefied petroleum gas is released from the cylinders through the holes in the burner. On complete combustion, it produces a clear blue flame. If the supply of oxygen is limited, the same flame turns yellowish and sooty.

Why is a Combustion Reaction an Oxidation Reaction?

As we already know, a combustion reaction cannot proceed in the absence of oxygen. For burning or combustion to take place, oxygen should be essentially present because it is the only gas that supports burning. A combustion reaction will always occur when a substance reacts with oxygen to release energy. For example, when methane burns in oxygen, it releases carbon dioxide and water. The formation of carbon dioxide shows the carbon present in the methane has undergone oxidation.

Combustion Equations

  • Methane is the major constituent of almost all hydrocarbons. Its combustion is represented by the following equation: 

CH4 + 2O2 -------> CO2+ 2H2O+ energy

  • Ethane is a saturated hydrocarbon. When it reacts with oxygen, it produces water and carbon dioxide. 

2C2H6 + 7O2 -------> 4CO2 + 6H2O + energy 

  • The food that we eat gets converted into glucose by the body. In the process of respiration, glucose is oxidized to produce carbon dioxide, water and energy. This energy is utilized for carrying out life processes. 

C6H12O6 + 6O2 ------> 6CO2+ 6H2O + energy 

Applications of the Combustion Reaction

Humans have been using the process of combustion for several millenniums. From cooking food to keeping the home warm, there are many major domestic and industrial applications of combustion.

  • In the steam engine, originally coal was burnt to heat water and produce steam. The jet of steam moved pistons that operated the machinery of the engine. Today, this same concept is used in operating thermal power plants.

  • Modern vehicles make use of internal combustion engines in which hydrocarbon fuels such as diesel, petrol, etc. are used to move the vehicle.

  • The process of combustion is widely used in explosives.

  • Rocket propulsion is based on the principle of combustion. A liquid or gaseous propellant is filled in the engine of the rocket. On combustion, several products are ejected from the combustion chamber at very high velocities. This provides a thrust for the rocket to take off.

  • In the metallurgy industry, the process of combustion is used in furnaces for purifying metals. 

Harmful Effects of Combustion

In the process of combustion, the chemical energy stored in fuel is converted to heat and light. Combustion is used to move locomotives, vehicles, machinery in industries and for a variety of other purposes. The smoke released from burning pollutes the atmosphere. The number of industries is increasing day by day. As a result, the continuous burning of fuels and the release of smoke from the chimneys and vehicular exhausts are adding up to the carbon dioxide in the atmosphere, thereby disturbing its original composition. 

Carbon dioxide and other products of combustion are greenhouse gases that trap solar radiation and increase the temperature of the earth, leading to a serious problem called global warming. If combustion does not take place efficiently, harmful products such as carbon monoxide and particulate matter are also released. Oxides of sulfur, nitrogen and other organic compounds lead to the formation of ozone and smog on the ground level. The burning of fossil fuels is the biggest contributor to air pollution. The efficiency of internal combustion engines can be increased by installing catalytic converters. Chimneys should be fitted with electrostatic precipitators so that the emanating smoke does not cause as much pollution as it otherwise would.

FAQ (Frequently Asked Questions)

Q1. What is Spontaneous Combustion? What is an Example of Spontaneous Combustion?

Ans: Spontaneous combustion is a reaction that takes place on its own without providing heat from any external source. This happens because some substances such as phosphorus and sulfur have a very low ignition temperature. In summers, when the temperature increases, these substances reach their ignition temperature at room temperature only. Hence, they start burning spontaneously without the application of heat. 

Q2. Most of the Elements Undergo a Reaction with Oxygen, But Why are All these Reactions not Considered Combustion?

Ans: Yes, it is indeed true that most of the elements undergo a reaction with oxygen. However, these reactions are termed as oxidation and not combustion. For combustion to take place, the requisites are the release of heat, light, and energy. The heat released in this process makes the reaction quite violent and it has to be controlled in due time to prevent a dangerous fire from taking shape. The violent nature of combustion distinguishes it from oxidation.

Hence, it can be concluded that combustion is essentially oxidation, but all oxidations are not combustions.