[Chemistry Class Notes] on Physical and Chemical Aspects of Combustion Pdf for Exam

Combustion is a chemical reaction in which a substance reacts with the oxygen molecule to give off energy in the form of heat, which is known as combustion. In the combustion, process light is given off during the process either in a form of flame or as a glow. Some substances that are combustible are fuel, coal, and organic compounds. Combustion is an exothermic reaction. The energy is released during this process, therefore, called the exothermic process. The characteristics features of the combustion process are the emission of heat and light.

The lowest temperature at which a substance catches fire is known as the ignition temperature. The combustible substance cannot catch fire or burn as long as its temperature is lower than its ignition temperature. In this article, we have discussed the chemical and physical aspects of combustion.

Types of Combustion Reactions

The combustion process can be classified into two types, depending on the nature of the product formed.

1. Complete combustion

2. Incomplete combustion

Complete Combustion

In this type of combustion process the reactant burns in the presence of oxygen or in an open environment. The final product obtained in the complete combustion is carbon dioxide and a water molecule. In this process hydrocarbon generally burns in the presence of oxygen to yield carbon dioxide and water. The reaction to this type of combustion process is given below:

C₂H₆ + O₂ → CO₂ + H₂O

However, the combustion process is not always very efficient. Sometimes the reactant undergoes an inefficient process and releases harmful products and byproducts. Generally, fossil fuels burn with the inefficient process of combustion.

Incomplete Combustion 

In this type of combustion process, the reactant burns in a limited amount of oxygen or in a sealed container. The final product obtained in this type of reaction is carbon monoxide and the other harmful products in the environment. This type of combustion leads to the major contribution of air pollutants. The major stable product of this type of reaction is carbon, carbon monoxide and hydroxyl radicals. 

In the Combustion Process, the Flames Can be Classified as:

1. Premixed flames

2. Diffusion flames

3. Oxidizing and reducing flames

Physical Aspects of Combustion

Let us discuss the physical aspect of combustion, in the combustion process the transfer of mass and energy takes place. This change takes place with the help of the diffusion process and the convection process occurs in the gases combustion. The rate of combustion is dependent on the pressure, temperature, and diffusion coefficient. The diffusion phenomena play an important role in the combustion process. Physical changes like sublimation and evaporation contribute to the ease of the combustion process. 

Chemical Aspects of Combustion

Let us discuss the chemical aspects of combustion, combustion is a complex chemical reaction process. It involves various steps. These steps are dependent on the chemical aspects of combustion undergoing substance. These steps are affected by the environmental surrounding factors like ignition temperature, heat, and light.

Steps involved in the chemical aspects of the combustion process

1. Attainment of the ignition temperature by the substance.

2. Spreading the heat from the ignition source to the adjacent layer of the substance.

3. This in turn leads to the ignition source for the next adjacent layer.

4. This process continues and the combustion gets completed.

Did you know that?

• The engines of the car and the engines of the rocket both work by the combustion process.

• Do you know that during the combustion process the fuel reacts with the oxygen molecule present in the atmosphere and the heat to release energy.