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Difference between Endothermic and Exothermic Reactions

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Chemical reactions on the heat involved are classified into two categories, Endothermic Reactions, and Exothermic Reactions. The difference between these reactions is that the first absorbs heat and the latter releases it.

In this article, we will learn about endothermic reactions, exothermic reactions, and their differences in detail.

Endothermic Reactions

Endothermic reactions are defined as those in which heat is absorbed. When nitrogen and oxygen are heated to around 3000°C, they combine to generate nitrogen monoxide, and a significant amount of heat is absorbed in the process.

N2            +            O2                       2NO
           (Nitrogen)                (Oxygen)            (Nitrogen monoxide) 

Since heat is consumed in the reaction between nitrogen and oxygen to generate nitrogen monoxide, it is an endothermic reaction. On the reactants’ side of an equation, write “+Heat” and “+Heat energy” or just “+Energy” to indicate an endothermic reaction.

The image given below shows the potential energy and rate of reaction curve of the Endothermic Reactions.

Endothermic Reactions

 

Here ∑HP and ∑HR are the sums of enthalpies of the products and reactants, respectively, and ΔH is the change in the enthalpy during a reaction, i.e., ΔH = ∑HP – ∑HR. Ea is the activation energy of the reaction.

Examples of Endothermic Reactions

Various examples of Endothermic reactions are,

Heating of Calcium Carbonate

When calcium carbonate is heated, for example, it decomposes into calcium oxide and carbon dioxide.

CaCO3         +       Heat          →         CaO         +         CO2
  (Calcium carbonate)                             (Calcium oxide)        (Carbon dioxide)

Since heat energy is absorbed in the decomposition of calcium carbonate, it is an endothermic reaction.

Photosynthesis Reaction

Photosynthesis is an endothermic reaction, where green plants absorb sunlight in presence of carbon dioxide, and water gives carbohydrates and oxygen as products.

6CO2  + 6H2O + sunlight   →   C6H12O6 + 6O2

The endothermic reaction can be written as follows in a chemical equation:

Reactants  +   Energy      →     Products 

Endothermic reactions are chemical processes in which the reactants absorb heat from the surroundings. These reactions cause a cooling effect by lowering the temperature of the surrounding environment.

Endothermic reactions are characterized by the creation of chemical bonds as a result of heat absorption from the environment. Exothermic reactions, on the other hand, involve the release of heat energy generated by the bond breakdown.

The energy change or enthalpy change in an endothermic reaction is positive, i.e., ΔH > 0.

Exothermic Reactions

A chemical reaction that involves the release of energy in the form of heat or light is known as an exothermic reaction. For example, when carbon burns in presence of oxygen to make carbon dioxide, a large amount of heat is produced.

C         +         O2         →              CO2        +       Heat

   (Carbon)           (Oxygen)              (Carbon dioxide)

Since heat is produced during the combustion of carbon in oxygen, it is an exothermic reaction. On the products’ side of an equation, use “+Heat” or “+Heat Energy” or simply “+Energy” to indicate an exothermic process. 

The image given below shows the potential energy and rate of reaction curve of the Exothermic Reactions.

Exothermic Reactions

Here ∑HP and ∑HR are the sums of enthalpies of the products and reactants, respectively, and ΔH is the change in the enthalpy during a reaction, i.e., ΔH = ∑HR – ∑HP. Ea is the activation energy of the reaction.

Examples of Exothermic Reactions

Various examples of Exothermic reactions are,

Burning of Natural Gas

Methane is the major component of natural gas. When natural gas is burned in the presence of oxygen in the air, carbon dioxide and water vapour are produced. There is also a significant amount of thermal energy produced.

The following is an example of how this could be expressed:

CH4                +               2O2                →               CO2             +            2H2O         +        Heat energy 
    (Methane)                        (Oxygen)                        (Carbon dioxide)           (Water)                                                

Since heat is produced during the combustion of natural gas, it is an exothermic reaction. Exothermic reactions characterize all combustion reactions. For example, the combustion of fuels such as wood, coal, kerosene, gasoline, and diesel, are all exothermic reactions since they produce heat energy.

Breaking of Food

Food is broken down into simpler components during digestion. The main component of food is carbohydrates and it is found in chapati, bread, rice, and potatoes. Carbohydrates are broken down into simple carbohydrates called glucose during digestion.

In a process known as respiration, this glucose is slowly burned by mixing with oxygen in our body’s cells to make energy. This energy also keeps our bodies warm, among other things. During respiration, glucose interacts with oxygen in our body’s cells to produce carbon dioxide, water, and energy.

C6H12O6    +       6O2       →         6CO2           +     6H2O           +       Energy

These reactions are the polar opposites of endothermic reactions, and they can be written as follows in a chemical equation: 

Reactants       →         Products      +       Energy

As a result, it’s easy to see how the net amount of energy required to start an exothermic process is less than the net amount of energy released.

The changes in enthalpy for an exothermic reaction will always be negative., i.e. ΔH < 0.

Difference between Endothermic and Exothermic Reactions

The following table gives the difference between Endothermic and Exothermic Reactions,

Exothermic Reaction

Endothermic Reaction

A reaction that releases heat as a type of energy from the system.A reaction in which the system absorbs energy in the form of heat from its surroundings.
The system’s energy is released into the environment.The energy from the surroundings is absorbed into the reaction.
Heat, electricity, light, and sound are forms of released energy.Energy is absorbed in form of energy.
Examples include rusting iron, settling, chemical bonds, explosions, and nuclear fission.Examples include ice melting, evaporation, cooking, gas molecules, and photosynthesis.

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FAQs on Endothermic and Exothermic Reactions

What are Endothermic Reactions?

The reactions which involve the absorption of heat or energy from the surroundings are called Endothermic Reactions. Example of endothermic reactions is the heating of Calcium Carbonate, photosynthesis, etc.

What are Exothermic Reactions?

The reactions which involve the release of heat or energy in the surrounding area are called Exothermic Reactions. Example of exothermic reactions is the burning of fuel, the breakdown of food, etc.

What is the Enthalpy of a Reaction?

The heat energy change that occurs when a reaction is completed, i.e., reactants become products is called the enthalpy of a reaction. It is denoted by ΔH and if ΔH is positive then heat is absorbed during the reaction and if ΔH is negative heat is released during the reaction.

What is the difference between Exothermic and Endothermic Process?

The basic difference between exothermic and endothermic reactions is that first absorbs energy from the surroundings in the form of heat and in exothermic reactions energy is released to the surroundings in the form of heat, respectively.

Why is Respiration regarded as Exothermic Reaction?

During respiration, glucose interacts with oxygen in our body’s cells to produce carbon dioxide and water, as well as energy.

C6H12O6  +  6O2   →    6CO2  +  6H2O  +  Energy

Since energy is produced throughout the process of respiration, as shown in the above reaction, so it is an exothermic process.

Why does the Neutralization Reaction’s Temperature rise?

When the temperature of a system rises due to heat transfer, it is called an exothermic process. Since neutralization processes are often exothermic, this heat is released into the environment, and hence the temperature of the neutralization reaction rises.

What are Examples of Endothermic Reaction?

Some of the endothermic reactions are photosynthesis proess, breathing of human being, evaporation process, melting of ice, etc.

Why is Heat Released or Absorbed in a Chemical Reaction?

Heat is released or absorbed in a chemical reaction due to changes in the energy of the molecules involved. When bonds are formed, heat is released (exothermic), and when bonds are broken, heat is absorbed (endothermic). This change in energy is a fundamental aspect of chemical reactions.



Last Updated : 06 Feb, 2024
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