What is an Exothermic Reaction?

Every single change that you observe in nature is the result of an energy change. Energy is a quantity which takes various forms and any action or change is triggered by the flow of energy. In chemistry, one studies various types of chemical reactions. Chemists have found that heat exchanges always accompany a chemical reaction and they can be classified according to the kind of heat or energy change that they trigger.

The motive force for every change that occurs in the universe can be attributed to some kind of energy change. If you observe the world around you, all kinds of biological and environmental changes that we see happening around us can be attributed to chemical reactions, which are powered by subtle inputs and outputs of energy.

What is Meant By an Exothermic Reaction?

Although you may not know what exactly is an exothermic reaction, you will certainly have experienced the effect of such reactions in your day-to-day life. To put it in simplest of words, 'An exothermic reaction is one which is accompanied with an emission of energy.'. Here 'Exo' means out or outside and 'thermic' is a word for heat. If you split the word this way, it's easier to remember what it means. A crackling fireplace gives you heat, because combustion is an exothermic phenomenon, emitting energy in the form of heat and light.

Since there are different forms of energy, this emitted energy may manifest itself in many forms, including heat, light and even sound. There are various types of chemical reactions in nature which are of an exothermic character. Every exothermic reaction is accompanied with an increase in temperature as heat is released to the surroundings.

Since heat energy is released through the reaction, there is an increase in the entropy of the entire system, along with a decrease in enthalpy (measure of internal energy of a system) associated with it. Nature prefers low energy states and therefore the release of energy is essential in some chemical reactions to attain stability.

Difference Between Exothermic and Endothermic Reactions

While exothermic reactions release energy, reactions with an endothermic character absorb energy. Without a certain amount of energy being absorbed, these reactions may never occur. While exothermic reactions tend to be spontaneous, endothermic ones need an influx of energy for them to occur.

Examples

Here are a few representative examples:

• Combustion of gasoline in car engines
• Corrosive reactions like metal oxidation
• Burning of any substance in air
• Chemical reaction which causes cement and concrete to set after mixing
• Rusting of Iron
• Reaction of any concentrated acid with water
• Ammonia production through Haber Bosch process

To conclude, an exothermic reaction is any chemical reaction that provides an energy output, as opposed to endothermic reactions which absorb energy. Most combustible chemical reactions are exothermic, which explains why they are used as energy sources.