Real Life Examples of Exothermic Reactions for IIT JEE

What is Exothermic Reaction?

Exothermic reaction lets out heat when the temperature of the surrounding objects goes on increasing. But this process takes up the heat and makes the objects in the surroundings cool. On the other hand, the endothermic process takes up the heat and makes the surrounding atmosphere cool.

Exothermic is basically produced from a Greek word, ‘Exo’ meaning exterior, while ‘thermic’ means ‘heat’. In the chemical process, exothermic means heat moving outside. The exothermic reaction is a heat generating chemical reaction.
Exothermic reactions generally take place in different day-to-day real life activities. Here are some of the examples of exothermic reaction:

1. Making of an ice cube

Making ice cube is a process of liquid changing its state to solid. Let's check this process, starting with water. A cup of water contains a large number of small particles of H2O molecules. Each small particles of H2O molecule is moving and has some amount of energy. When an ice cube tray, filled with water is placed in a freezer, it slowly loses heat and start to cool down to become ice cubes. Changing of water into an ice cube is an exothermic reaction. 
2. Snow formation in clouds

Snow formation in clouds is also an exothermic reaction. Clouds come into existence from condensation of water vapor. Some clouds have ice and there we get the heat from condensation as well as from crystallization. For exothermic reaction, it is the process that gives energy in the form of a heat body.

3. Burning of a candle

In the case of burning of candle, the body of the candle carries paraffin, which is a hydrocarbon. When paraffin burns with the flame, it reacts with oxygen to create carbon dioxide and water. This reaction is certainly exothermic as it gives out heat to the atmosphere with the help of other products. The amount of heat released depends on the chemical reaction between the hydrocarbon and oxygen.

4. Rusting of iron

The rusting of iron is a chemical reaction between iron & oxygen. When iron is in pure form or alloyed, rusting of iron takes place. In this process, heat gets released when iron comes in contact with oxygen. Basically, rusting is the formation of chemical substances that takes place due to the formation of moisture on the iron. For this reaction, the chemical formula goes as Fe2O3.xH2O.

5. Burning of sugar

Inside the human body, sugar is a chemical reaction. It is formed by combination of carbon, oxygen, and hydrogen. It releases heat once it goes inside the human body, resulting in the formation of energy. The heat goes out of the human body and gets added into the atmospheric heat. This process is called an exothermic reaction. But there are few doubts which make it an endothermic reaction. For instance, when we put sugar in a bowl and burn it by a flame, it starts generating heat. It releases a huge amount of energy which makes it an endothermic reaction. 

6. Formation of ion pairs 

When ions are in gaseous form, it makes interaction with water, resulting in hydrated ions. This is an exothermic process. The smaller the ion radius, the bigger is the ion charge. Consequently, ion hydration enthalpy grows larger resulting in a concentrated exothermic reaction.

7. Reaction of Strong acid and Water

As we know that heat is necessary to break a chemical bond. For example, Hydrogen chloride consists of a hydrogen atom H and a chlorine atom Cl connected by a covalent single bond which is a diatomic molecule.

HCl (Hydrogen chlorides) is in the form of a strong acid and when it gets mixed in water, the hydrogen ion reacts with water to make a more complex reaction. Since hydrogen ion is very tiny in size and a large amount of energy that is generated gets concentrated in a relatively smaller area. At this time, it draws the polar water molecules. The hydrogen ions results in the formation of a covalent bond with water and also attract a number of strong hydrogen bonds. So, this process is an exothermic process. 

8. Water and calcium chloride

Calcium chloride, water, and baking soda mixed together (the experiment is done by the students in their school labs) produce a rise in the temperature by letting off heat into the atmosphere. This process is also known as an exothermic reaction.

9. Cold packs to heal an injury

One other example of the exothermic reaction is a cold pack. If we apply a cold pack to the place of pain after an injury then it will be an exothermic reaction. The cold pack has two bags - an inner bag and an outer bag. The inner bag contains water in it while the outer bag has ionic salts. On pressing the cold pack, the water from the inner bag gets in touch with ionic salt and eliminates heat. Thus, the heat released to the atmosphere makes it an example of an exothermic reaction.

10. Laundry Detergent

Every time you don’t require a chemistry lab for experiments, sometimes things present around you are also useful for understanding the nature of reactions. The best example of this is the detergent powder. Simply dissolving laundry detergent in a bit of water generates heat. So, this is a process of exothermic reaction.

11. Nuclear Fission

Nuclear fission is a unique exothermic reaction in which the nucleus of a heavy atom splits into pieces such as lighter element and releases energy. In this process of Nuclear Fission, energy is released in the form of heat, kinetic energy and gamma photons which is a form of high energy radiation.

Heavy atomic nuclei are bombarded with free neutrons which break the nucleus apart in nuclear reactors and bomb. As a result, the fission reaction releases more neutrons. So this is an example of an exothermic reaction.

12. Combustion Reaction

Combustion is an example of exothermic reaction including materials like hydrocarbons reacting with oxygen to form combustion products such as water and carbon dioxide. Any combustion reaction is always involved with molecular oxygen O2.
For example, when wood burns, it must require the presence of O2 and a large amount of heat is produced. Wood is one of the common combustible item that is organic (a combination of carbon, hydrogen, and oxygen). 

13. Respiration

Respiration is the process of metabolic which is common in all living things. In this process, the living organism intakes oxygen and releases carbon dioxide. Food molecules get converted into simpler substances like glucose. Then glucose is combined with oxygen and it provides energy to our body. This is called the respiration process and respiration is an exothermic reaction. The chemical equation is shown below. 

C6H12O6 (aq) + 6O2 (g) 6CO2 (g) + 6H2O (l) +ENERGY

14. Thermite reaction

Basically, a thermite reaction is an iron oxide (rust) reacting with aluminum to produce molten iron. The reaction is started by the formation of heat from the burning magnesium ribbon which is placed in the iron oxide/aluminum mixture. It is the mixture of iron oxide powder, aluminum powder and starts reacting when it is heated. 

This reaction is an exothermic reaction and the equation is given below.

Fe2O3 + 2Al Al2O3 + 2Fe

15. Neutralization reaction 

In the process of neutralization reaction, an acid and a base react to form a salt and water. Also, in this reaction, the bonds are being made and energy is released to the surroundings. 

For example: The reaction between HCL (a strong acid) and NaOH (a strong base)

HCL (aq) + NaOH(aq) NaCL(aq) + H2O(l)
The complete ionic equation is –
H3O(aq) + CL-(aq) + Na(aq) + OH+(aq) Na+(aq) + Na+(aq) + Cl-(aq) + 2H2O(l)
The net ionic equation is regulated by removing the spectator ions (the ions present on both the reactants and the product side)
H2O+ (aq) + OH-(aq) 2H2O (l)

16. Barking Dog

It is an interesting exothermic reaction. In this reaction, you need a long glass tube, nitrous oxide and carbon disulfide. In case these chemicals are not available with you then there is an alternative solution – a bottle and rubbing alcohol. It is not as loud as the above reaction but it does produce a nice flame and an audible ‘woofing’ sound. 

17. Decomposition of vegetable 

Decomposition of vegetable is also an exothermic reaction because microbes need the energy to break the bond of vegetables that’s why it produces heat energy. This process is largely carried out by soil invertebrate fauna and this decomposition is known as exothermic reaction.

18. Solution of Sulfuric Acid in water

The processes of adding water into acid or an acid into water are both exothermic reactions. The reason behind this is a number of possible factors, including increased entropy, as you are breaking a bond of hydrogen and chlorine atoms in hydrochloric acid, making new ions namely free chloride and hydronium. 
The dissolution takes place in the two steps mentioned below:

Step 1
H2SO4 + H2O H3O + HSO4-
Step 2
HSO4- + H2O H3O+ + SO42