Exothermic Reaction

There is a basic difference between the mechanism and the process of exothermic and endothermic reactions. In the case of exothermic reactions, the particular system and the reactants of the system release heat into the surroundings and it cools down. In the case of endothermic reactions, the entire system and the reactants gain heat from the surrounding area and hence the system gets warmed up.

What is an Exothermic Reaction?

A reaction that is chemical in nature and is characterized by the release of energy in the form of heat or light is called an exothermic reaction. Matching a light using a matchstick is one example of this type of reaction where the release is in the form of both heat and light.

Compared to an endothermic reaction, where energy is absorbed, the exothermic reaction leads to the release of energy. This energy is often higher than the combined energy of the reactants. In the above example of the matchstick, the flame produced as a result of matching gives out higher energy than compared to the potential energy of the matchstick.

The energy dissipated in an exothermic reaction is transferred into the surroundings. Therefore, the change in enthalpy (a quantity that measures the heat content of a system by calculating the change in energy) is negative in such a reaction.

Enthalpy

Enthalpy is a thermodynamic quantity used to measure energy change in a given reaction. Since it is not technically feasible to measure how much energy is dissipated in a reaction, the change in energy is measured instead. It is calculated by finding the difference between the energy of the products reacting and the energy released after the reaction.

For an exothermic reaction, since the dissipated energy is always higher, this quantity has a negative value. Enthalpy is denoted as ∆H.

Above is an energy level diagram that describes an exothermic reaction. The difference in intrinsic energy of the products and the reactants showcase how much energy is given out to the surroundings.

Examples of Exothermic Reactions

Following is a list of examples of endothermic reactions that are found in day to day life:

• Firing a Firecracker – the bursting of a firecracker gives out a loud noise in addition to light and heat, being one of the best examples of an exothermic reaction.

• Lighting a Candle – this is a continuous reaction where the wax acts as fuel and creates a flame for a long period of time.

• Lighting a Light Bulb – the electric current causes the reaction in the tungsten filament and gives rise to both light and heat

• Burning of Fuels – whether it is a car’s engine or a gas stove, burning of fuels is also an exothermic reaction. The generated heat is used for purposes ranging from driving a motor, cooking, etc.

• The Burning of Hydrogen in Hydrogen-oxygen fuel cells is a type of exothermic reaction as it undergoes combustion and produces an electric charge

• The burning of natural gas methane is also an example of an exothermic reaction. Given below is the reaction in the form of an equation

CH4+2O2CO2+2H2O

There are many more examples of such a reaction that can be found in the surroundings. The key is to look at whether these reactions release energy into the environment and if it is in the form of light, heat, or in some cases, sound. Some of the other, advanced types of such reactions are acid and alkali neutralization reactions, water and reactive metals, and mildly reactive metals with acids that are strong in nature. Exothermic reactions are also used for the purpose of self-healing technology.

In the above list, the reaction in the first two examples can also be called combustion. Let’s find out more about this concept.

Combustion

The concept of burning where a fuel undergoes reduction and causes oxidation to let out some energy in some form is called combustion. Putting unwanted papers into fire using some kerosene and a matchstick is an example of combustion. In other words, anything that burns and which lets out energy can be called combustion.

In most types of combustion, oxygen plays an important part as an oxidizing agent as it is an important element in burning. However, it also gives out harmful by-products such as smoke and ash. Such by-products are one of the most ubiquitous causes of air pollution.

In late 2019, the stubble burning carried out by farmers in some of the northern states of India led to the production of smog (a combination of smoke and fog) in large amounts. This had an adverse impact on the atmosphere of the state of New Delhi, causing its air quality to drop to an alarmingly low level.

Detonation of Nitroglycerin  

Nitroglycerin is a combustible substance actively used in the production of explosives. Its extremely volatile physical properties, which lets it catch fire easily and almost instantaneously, makes it a sought-after element for explosives and dynamite. It is usually used along with another fuel for combustion.

When nitroglycerin is detonated, it causes the surrounding fuel to burn, which in turn, creates a shockwave that can propagate at a speed that is 30 times that of sound. The detonation itself is an example of an exothermic reaction as it releases voluminous gases and a very high temperature (upwards of 5,000 degrees Celsius).

The physical characteristics of nitroglycerin let itself decompose during combustion and create large amounts of energy. This is why it is the preferred ingredient in high explosives.

Nuclear Fission of Uranium-235

The fission of Uranium-235 is another example of an exothermic reaction. When the fission happens, it releases energy in the form of heat and gamma rays. This energy has several uses across various industries. The reaction also results in nuclei and neutrons which need to be discarded properly to avoid contamination of the surroundings.

The nuclear fission of Uranium is a high-profile reaction and has to be carried out under controlled environments. It is also one of the most efficient ways of disseminating energy as it is known to produce 2.5 million times the energy produced through coal burning which is one of the most common types in the world today.

Neutralization Reactions

These are reactions where the elements participating in the combustion are acidic and basic. This results in the formation of by-products such as salt and water. Since they neutralize the pH of the reacting elements they are known as neutralization reactions.

Why is Respiration an Exothermic Reaction?

The action of respiration involves the intake of oxygen. This oxygen then undergoes a reaction with glucose, giving out carbon dioxide, water, and energy. While water and carbon dioxide are by-products, the energy that is used by the lungs and heart to pump blood and various organ-related activities confirm that it is an exothermic reaction.

Remember that it is not dependent only on participants that a reaction is labelled exothermic or endothermic. It is the output also. 

What is the Importance of Learning the Concept of Exothermic Reactions?

Learning the concept is not only important for the students of Physics but also the students who want to pursue their higher studies in Chemistry also need to learn about these reactions. Understanding these reactions will help the students to identify the distinguishable characteristics exhibited by the different components that are responsible for giving birth to a particular reaction.

Moreover, the students of Chemistry should have detailed knowledge about the characteristics of each of the chemicals that play a significant role in the occurrence of the reaction. Since exothermic and endothermic reactions cannot happen at the same time, the students need to gain information about these two reactions in detail.

The symbols that signify some important information about a particular chemical reaction play a great role. Understanding the significance of the symbols can make the learning process easier for the students because these symbols can easily interpret the significance of the reaction.

There are separate articles published on the website of Vedantu that discuss the key information about exothermic and endothermic reactions. The students can also communicate with the expert trainers by joining the free classes and learning the basics about these reactions. The students also need to learn about the various stages of exothermic reactions like freezing, deposition, etc. Downloading the course materials from the website is free.