Definition of Exothermic and Endothermic: Characteristics, Theory, and Examples

Definition of Exothermic and Endothermic – Especially for Readers who have graduated from high school or are still in high school, chemistry is one of the subjects that must be studied. For most people, chemistry is a difficult subject to understand.

Although chemistry itself is very easy to find in everyday life. In fact, there are also many chemistry that can explain various phenomena in human life.

Just a reminder, you should know that in this chemistry subject there is a learning material that discusses the heat of a substance that accompanies a chemical reaction which is known as thermochemistry.

An example of a discussion in thermochemistry is the process of burning firewood. In the burning process, the wood that is burned and the environment around it have different temperatures. This difference eventually causes the transfer of energy from objects with higher temperatures to objects with lower temperatures.

This energy transfer will continue until the wood and the environment are at the same temperature. This transferred energy is also known as heat. The heat change will be expressed in an enthalpy change (∆H).

Now, if you look at the enthalpy change, chemical reactions can be divided into two parts: exothermic reactions and endothermic reactions.


In order for you to understand more deeply about exothermic reactions, it is important for you to know thermochemistry. In short, thermochemistry is a science that discusses changes in heat (heat) of a substance that involves physical and chemical processes.

Thermochemistry enters into the section on thermodynamics which discusses energy changes in a chemical reaction and is manifested as the heat of reaction. The particles that make up the substance continue to move consistently resulting in kinetic energy. And this kinetic energy is directly proportional to the absolute temperature.

In other words, when an object is hot, its constituent atoms and molecules move quickly so that the kinetic energy generated is also large. The potential energy of the substance comes from the attractive and repulsive forces that occur between the particles that make up the substance. The most common form of energy is heat energy.

While heat itself is a form of energy that can be exchanged between the environment and the system. While the heat of reaction is the change in energy in a chemical reaction in the form of heat.

In general, to be able to detect heat in an object, you can measure the temperature of that object. If the temperature is high then the heat inside is also large, conversely if the temperature is low then the amount of heat is also small.

The tool that can be used to measure it is called a calorimeter. This tool utilizes the technique of mixing two substances in a container. The calorimeter is usually used to determine the heat of a substance. There are two types of calorimeters that you can use, namely the constant pressure calorimeter and the constant volume calorimeter.

Thermochemistry itself is an example of applying the laws of thermodynamics to chemical events that study heat in chemical reactions. Thermochemistry can also be interpreted as a science in chemistry that studies changes or dynamics in chemical reactions by simply observing heat.

An example of the application of this science in everyday life is the chemical reaction that occurs in the human body when producing energy needed for all daily activities. Or burning coal which is used to generate electricity.

You can find and also learn other terms in chemistry easily through Manihar Situmorang’s Environmental Chemistry book. Especially those related to chemicals, the composition of water and eels, drinking water treatment, water pollution, and so on.

Definition of Exothermic and Endothermic

1. Definition of exothermic

The term exothermic itself is taken from the Greek, namely exposed (outside) and also term (heat or heat). Therefore exothermic can be interpreted as a chemical reaction that can produce heat. This reaction occurs because of the transfer of heat (heat) from the system to the environment which causes the environment to become hotter.

Exothermic reactions can occur naturally (naturally) and also artificially (intentionally). Examples of natural exothermic reactions that occur in nature are burning wood, running water, or rusting iron.

While artificial (deliberate) exothermic reactions usually occur in the laboratory which are the result of an experiment. For example, a mixture of water and concentrated acid, the reaction of water and sodium peroxide, the reaction that occurs between HCl and zinc powder, or something else.

Even so, generally exothermic reactions occur just like that or spontaneously. Such as glucose fermentation or ethanol manufacture. Another example is the reaction that occurs in the formation of NaCl.

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

In this sequence of reactions, the reactants are HCl and NaOH solutions. While the products are a solution of NaCl and H2O.

2. Definition of Endotherms

Just like exothermic, the term endotherm is also taken from the Greek words endon (in) and also term (heat). In other words, an endothermic reaction means a reaction in which heat from the environment enters the system. In short this is a reaction that absorbs heat.

In this endothermic reaction, heat is transferred from the environment to the system causing the temperature of the region to decrease and become colder. Because this endothermic reaction absorbs energy, it can cause the energy of the system to increase. Therefore the enthalpy also increases so that the change has a positive sign.

One example of an endothermic reaction in everyday life is photosynthesis. In this event, the trees absorb heat from the sun which then increases the enthalpy of the reaction.

System and Environment

In the discussion of the terms exothermic and endothermic above, you will find the terms “system” and “environment”. So what exactly is meant by the system and the environment itself? Here’s an explanation.

The term system is generally used in the process of analyzing energy changes associated with chemical reactions. The system is defined as that part of nature that is of concern to humans.
Meanwhile for chemists, systems are generally substances involved in physical and chemical changes. The remainder of nature that exists outside the system is then known as the environment or surrounding.

For example the reaction between water and calcium metal in a beaker. Water and calcium metal are part of the reaction system while the beaker, air pressure and air temperature are the environment.

Kinds of systems

Based on interactions with the environment, systems in chemistry can be classified into three types, namely open systems, closed systems, and isolated systems.

1. Open System

An open system is a system resulting from the transfer of energy and matter that occurs due to the interaction of the system with the environment. An example is the process of dissolving table salt in an open beaker.

2. Closed System

In a closed system, material transfer is not possible, but energy transfer can still occur between the system and its surroundings. For example, when observing the dissolution above, in this situation the material cannot get out or enter the glass beaker because the glass beaker is closed.

Even so, energy can still enter and leave the glass beaker. This is usually indicated by the presence of heat attached to the walls of the glass beaker. Or it could also be that the heat energy is channeled into the system by heating it over a burning fire.

3. Isolated System

While an isolated system is a system that does not support the transfer of matter or energy between the system and the environment. Like for example hot water in a thermos. The water is put in a thermos so that the heat does not dissipate and the volume of water remains constant. In other words, neither the heat nor the water undergoes a change.

Readers can also find a complete discussion of systems and the environment in chemistry in the book Fundamentals of Physical Chemistry by Don Shillady. This book has quite a lot of advantages such as a more interesting presentation, can be used as a guide to understand the principles of mathematical derivatives, and easy-to-understand explanations.



Characteristics of Exothermic and Endothermic Reactions

To identify an exothermic reaction, you can rely on its characteristics as follows:

  • The system absorbs heat from the surroundings
  • The surroundings absorb heat from the system
  • The surroundings and the system have the same amount of heat
  • When the ambient and system heats are added together, the result is zero
  • At the end of the reaction, the heat in the environment is always less than the heat in the system
  • Usually the sum of the enthalpies in the product value is less than the enthalpy of the reaction.
  • The enthalpy change has a negative value
  • When the system is releasing energy, the temperature increase can be seen by increasing temperature or fire. and when the heat is stopped, the reaction will still go on.

Like exothermic reactions, endothermic reactions also have their own characteristics. Here are some of its features:

  • The products have more energy than the reactants
  • The formation of chemical bonds can release energy
  • The bond energy in the products is greater than in the reactants
  • The enthalpy change is negative

Exothermic Reaction Theory

Combustion, fermentation or other chemical reactions date back to ancient times. The ancient Greek philosophers were figures who developed theories about these chemical reactions.

For example, Empedocles with his theory of the four elements. He said that every material has four basic elements namely earth, air, water, and fire. In medieval times, chemical transformations themselves were usually studied using alchemists.

An example is turning lead into gold by utilizing the reaction that occurs between lead and a mixture of sulfur and copper.

Many scientists are also trying to produce non-earthly chemical compounds such as nitric acid, and sulfuric acid synthesis. This process was carried out by the alchemist Jabir ibn Hayyan. He tried to heat sulfur and nitrate minerals.

Then in the 17th century, Johan Rudolph Glauber succeeded in producing hydrochloric acid and sodium sulfate by reacting sodium chloride with sulfuric acid. Later in 1746, a development of the lead chamber process was carried out and also the Leblanc process was able to produce large quantities of sodium carbonate and sulfuric acid. So that chemical reactions become possible in industry.

In the 1880s, advanced sulfate-origin technology was first introduced and from 1909 to 1910 the Haber process was developed for the synthesis of ammonia.

In the field of organic chemistry, it is believed that it is impossible for any compound found in living organisms to be obtained by chemical synthesis processes. Based on the concept of vitalism, these organic compounds have been endowed with “essential skills different from organic matter.”

Then Friedrich Wohler succeeded in solving this concept in 1828 with his urea synthesis. Other chemists who also contributed to the field of organic chemistry were Christopher Kelk Ingold with the Subs reaction mechanism and also William Williamson with the synthesis of ethers.

Examples of Exothermic and Endothermic Reactions

The easiest example of an exothermic reaction is a campfire. When you burn wood to make a bonfire, the heat released into the environment can make your body warmer when you are around the firewood.

Besides that, there are also other examples that can be found in everyday life, such as the eruption of fireworks which always celebrate the turn of the year.

While the most common and widely used example for defining an endothermic reaction is the process of frying tempeh in cooking oil using a frying pan. In this process, the system is tempeh, while the environment is cooking oil and air. While the type of system is open.

As time goes by, the fried tempeh will gradually get hotter. This means that tempeh gets heat from its environment, namely cooking oil, although some of the heat escapes into the air.

In this process there is a transfer of matter and heat from the system to the surroundings, therefore the system is an open system. The flow of heat transfer is that the fire transfers the heat to the pan, then the pan gives the heat to the cooking oil, and the cooking oil transfers the heat to the tempeh.

Difference between Exothermic and Endothermic Reactions

The first difference between exothermic and endothermic reactions is the enthalpy change. In an exothermic reaction, the change is negative. These changes are usually calculated by Hess’s Law. The law says that enthalpy is directly proportional to the change in temperature.

The temperature drop that occurs in an exothermic reaction can change the temperature to negative. As a result, the enthalpy change will also have a negative value. While the change in enthalpy in an endothermic reaction is positive because there is an increase in temperature resulting in a positive temperature change.

Other differences regarding exothermic reactions and endothermic reactions that you should know are as follows:

Exothermic Reaction:

  1. There is liberation of heat
  2. The system temperature level is higher than the environment
  3. The position of heat is transferred from the system to the surroundings
  4. The enthalpy of the system decreases
  5. There is an increase in temperature

Endothermic Reaction

  1. Requires heat to be absorbed
  2. Ambient temperature level is lower than system temperature
  3. The position of heat is transferred from the surroundings to the system
  4. There is a drop in temperature

Thus a complete explanation of the meaning of exothermic, system and environment, characteristics of exothermic reactions, theory and examples. By knowing these things you will automatically increase the knowledge you have. Mainly in the field of chemistry. One of the subjects that is considered difficult to learn by students and students. See you in the next article, okay!