As we know in a chemical reaction either the energy is released or absorbed. The chemical reaction converts one set of chemical substances (reactants) into another (resultant). Chemical reactions are usually represented in the form of a chemical equation. A chemical reaction prepares the constituent atoms of the reactants to create different substances as products. It is necessary for a chemistry student to know the cause of the reaction, the catalyst that acts, the process involved and various theories like Valence Bond Theory and molecular orbital theory. Some chemical reactions are spontaneous and some take places slowly. There are many chemical reactions that take years to attain equilibrium like radioactive reactions, rusting of iron and many more.
Depending on the nature of the chemical reaction it is classified into
- Endothermic reaction
- Exothermic reaction
Endothermic Reaction: As the name suggest endo means within, therm refers to “hot” or “warm”. An endothermic reaction is a type of reaction which requires or absorbs energy from its surroundings, in the form of heat. A large amount of energy in the form of heat is released in this process. This reaction involves the breaking of the existing chemical bonds and forming new chemical bonds. It requires input energy or takes in energy to continue the process.
Example: melting of ice, dissolving sugar in water, photosynthesis process and many more.
Exothermic reaction: It is a process that releases energy in the form of light or heat. It is a reaction that is opposite to endothermic reaction since the energy is transferred into the surroundings rather than absorbing energy from the surroundings. Hence, change in enthalpy (ΔH) will be negative. It is generally represented as reactants → products + energy.
Example: It involves from the burning of a candle to the nuclear fusion reactions.
Combustion is an ideal example of Exothermic reaction and is known as the burning process. In a combustion reaction, fuel undergoes reduction when exposed to an oxidizing agent (oxygen is the commonly found oxidizing agent in the atmosphere) and forms an oxidized product.
Example: combustion reaction of methane
CH4 + O2 → CO2 + H2O + Heat
Nuclear fission reaction of uranium-235 is an ideal example of Exothermic reaction.
In this reaction, one atom of uranium-235 releases more than 2.5 million times the energy that is produced from the combustion of coal. To know more about different types of chemical reactions with examples and also know about Valence Bond Theory, visit and Subscribe BYJU’S YouTube Channel.