Short Answer

An exothermic reaction is a chemical reaction that releases energy in the form of heat, light, or sound. In this reaction, the energy of the products is lower than the energy of the reactants because excess energy is given out to the surroundings. As a result, the temperature of the surroundings increases.

Exothermic reactions are common in everyday life. Burning fuels, respiration in living organisms, and the reaction between acids and bases are examples of exothermic processes. These reactions are important because they provide heat, energy, and support many natural and industrial activities.

Detailed Explanation :

Exothermic reaction

An exothermic reaction is a type of chemical reaction in which energy is released into the surroundings. This energy usually appears as heat, but sometimes it may also be released as light or sound. The key feature of an exothermic reaction is that the total energy of the products is less than the total energy of the reactants. The difference in energy is released during the reaction, which makes the surroundings warmer.

During any chemical reaction, bonds between atoms break and new bonds form. Breaking bonds requires energy, whereas forming new bonds releases energy. In an exothermic reaction, the energy released when new bonds form is greater than the energy needed to break the original bonds. Because of this, extra energy is released outwards, causing a rise in temperature.

A simple example is the burning of wood or coal. When wood burns, it reacts with oxygen to produce carbon dioxide, water, and a large amount of heat. This heat warms the surroundings and shows that the reaction is exothermic. The same principle applies to burning fuels like petrol, LPG, and natural gas.

Another example is the reaction between water and quicklime (calcium oxide). When water is added to quicklime, a large amount of heat is produced, making the container hot. This reaction is commonly used in construction to prepare slaked lime.

Characteristics of exothermic reactions

Exothermic reactions have some common characteristics that help identify them:

• Release of heat:
  The most noticeable feature is the increase in temperature. The surroundings become warm or even hot.
• Energy decreases in the products:
  Products have lower energy. The extra energy is released, making the reaction exothermic.
• Often fast reactions:
  Many exothermic reactions occur quickly, such as burning.
• Formation of stable products:
  The products formed are usually more stable and have stronger bonds than the reactants.
• Energy is shown with a negative sign:
  The energy change (ΔH) in exothermic reactions is negative, meaning energy is lost to the surroundings.

Examples of exothermic reactions

1. Combustion:
   Burning of fuels like wood, LPG, petrol, or kerosene releases a large amount of heat and light.
2. Respiration:
   Living organisms break down glucose in the presence of oxygen to release energy.
   Glucose + Oxygen → Carbon dioxide + Water + Energy
3. Neutralization:
   When an acid reacts with a base to form salt and water, heat is released.
4. Rusting of iron:
   This is a slow exothermic reaction where iron reacts with oxygen and moisture.
5. Thermite reaction:
   Aluminium reacts with iron oxide to release a large amount of heat used for welding.

Importance of exothermic reactions

Exothermic reactions are extremely useful in many fields:

• Daily life:
  They provide heat for cooking and warming homes through burning fuels.
• Biological processes:
  Respiration is exothermic and provides energy for all living activities.
• Industry:
  Many manufacturing processes depend on exothermic reactions for heat.
• Construction:
  Slaking of lime produces heat needed for preparing building materials.
• Chemical hand warmers:
  Some hand warmers work on exothermic reactions to provide heat in winter.

These reactions help maintain energy balance in nature and support essential functions such as maintaining body temperature.

Conclusion

An exothermic reaction is a chemical reaction that releases heat, light, or sound energy into the surroundings. It occurs because the energy released during bond formation is greater than the energy absorbed during bond breaking. Such reactions play an important role in daily life, industry, agriculture, and natural biological processes. Understanding exothermic reactions helps explain how energy flows in chemical systems and why some reactions feel warm or hot.