Energy is released in an exothermic reaction.
An exothermic reaction is a process that causes the release of energy . This released energy can be constituted as heat or light .
It should be noted that, when atomic nuclei undergo certain modifications or combine, a procedure known as a nuclear reaction develops. These reactions lead the nuclei to combine or fragment, which implies the absorption or release of energy and particles depending on the case.
There are different types of nuclear reactions, which can be very important at an industrial level for energy use. The one that implies that energy is released, as we already indicated, is known as an exothermic reaction.
Combustion, a common example of an exothermic reaction
Combustion is the most common example of an exothermic reaction. These reactions occur when an oxidizer reacts with a fuel, causing it to burn and, therefore, releasing energy in the form of light and heat. This means that, when we light a bonfire , we are causing an exothermic reaction.
It should be noted that combustion is a redox reaction . Therefore, we can say that reduction and oxidation processes generate exothermic reactions since they release high energy values.
The most common types of fuel are those organic materials whose content contains hydrogen and carbon. When the reaction is complete, all the elements that make up the fuel are oxidized one hundred percent. During combustion, water, carbon dioxide, sulfur dioxide (provided the fuel contains sulfur) and nitrogen oxides are formed (although this depends on the pressure, the amount of oxygen and the temperature).
Combustion is an example of an exothermic reaction.
The opposite process
We said above that nuclear reactions can release or absorb energy. By releasing energy, they are defined as exothermic reactions.
The opposite occurs when the reaction involves the absorption of energy: in this case, it is called an endothermic reaction . The generation of ozone in the atmosphere is an example of a reaction that absorbs energy and is, therefore, endothermic.
Exothermic reaction, solidification and condensation
When a matter in a liquid state becomes a solid state (that is, it solidifies ) and when a matter in a gaseous state becomes a liquid (it condenses ), an exothermic reaction also occurs. Let's look, therefore, in more depth at the concepts of solidification and condensation :
Solidification
It is a physical process through which matter goes from a liquid state to a solid state, as a result of its temperature being decreased or the matter being compressed. This change of state , in turn, opposes fusion , a process that, however, takes place at the same temperature. The most common example of solidification occurs when water freezes, something many people experience daily when they place a container of water in the freezer.
It is worth mentioning that the volume of water increases when it becomes a solid state, something that does not happen with other materials. Solidification is also the name given to the process through which certain materials, such as clay or cement, harden when dehydrated at a constant temperature . In any of these cases, we are faced with examples of exothermic reactions, included under the framework of solidification.
Condensation
This phase change implies that the matter goes from a gaseous state (usually in the form of vapors ) to a liquid. It is considered the inverse of the process called vaporization, the protagonist of most changes in the state of water. When the transition from a gaseous state to a solid state is direct, it is called deposition or reverse sublimation .
Although various factors influence the condensation process, such as temperature and pressure, it is usual to refer to a pressure level close to ambient pressure. If, on the other hand, a high overpressure is used to create the conditions necessary for the transition, we speak of liquefaction .