Difference Between Exergonic and Endergonic Reactions

Edited by Diffzy | Updated on: April 30, 2023

       

Difference Between Exergonic and Endergonic Reactions

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Firstly, we will be discussing free energy. What do you think "free energy" is? The solar panel gives out free electrical energy, or maybe a gas station gives out free gas. All of the preceding examples, however, are not examples of free energy, which we will discuss in this article. Instead, we will be learning about the type of free energy that is mostly associated with a chemical reaction, which will provide data on how much energy is released (or consumed) and the type of energy released when the chemical reaction takes place.

The metric required to capture the effect of a reaction on the entropy of the universe, including both the reaction (an exergonic and endergonic reaction) and its surroundings, is Gibbs free energy. The change in free energy gives us crucial information about the reaction's kinetics and spontaneity. Simply put, the changes in Gibbs' free energy from the beginning to the end determine the maximum usable energy released or absorbed. Whether the energy is absorbed or released determines the reaction's sign (positive or negative) and whether the reactions will be spontaneous or not.

The main focus of this article is the difference in Gibbs free energy between reactions. That is, the exergonic and endergonic reactions are the ones that occur when the Gibbs free energy travels from the initial stage to the final stage. Although it's not just about positive and negative signs and spontaneous and non-spontaneous, it is more about enthalpy, entropy, temperature, and pressure. All of the factors are important when considering the final reaction, we have.

We will learn the distinctions between the previously stated reactions and, most likely, understand what causes such reactions, what other factors besides those previously mentioned are considered, what specific examples of the reaction exist, and so on.

Exergonic Reaction vs. Endergonic Reaction

Energy is the ability to complete tasks. Energy can be converted from one form to another, such as heat, sound, light, and so on. For instance, when the temperature of the system changes or rises due to a change in reaction, the energy is thus transformed into heat. The situation is analogous to a chemical reaction, which is the process by which one or more compounds are converted into a new set of compounds through a series of changes. As the reaction is initiated, there will be changes from the system to the surroundings or vice versa. The result is, as above stated, spontaneous or non-spontaneous. As previously stated, the result is either spontaneous or non-spontaneous. Although not all of the reactions that occur in the environment are spontaneous, they are coupled to spontaneous reactions (which we will learn about in the following paragraph) and are equally driven by spontaneous reactions.

Moving further, as we all have learned, the exergonic and endergonic reactions are the chemical reactions, or processes, in thermodynamics (thermochemistry of physical chemistry). The names of reactions describe the obvious nature of the energy, whether it is released or absorbed. The classification of the reaction is related to an endothermic and an exothermic reaction; the only exception is that the endothermic and exothermic reactions describe what happens with any kind or form of energy, whereas the endothermic and exothermic reactions are only related to heat or thermal energy.

These two chemical reactions are defined according to changes in Gibbs free energy. The difference is easily caught in the names of the reactions. That is, the word endergonic is derived from Latin, bifurcated as the word "ender," which is sub-derived from "endo," which means "within." This makes it clear that the other word, exergonic, is defined as external.

As per the above-stated thesis of reactions, an endothermic reaction is a chemical reaction that absorbs heat energy and has a positive sign of free energy. Moving on, an exergonic reaction is a chemical reaction that produces heat with a negative sign of free energy.

This is only a basic definition and distinction between chemical reactions; more detailed concepts of both reactions, reactions' effects, and distinctions will be covered in subsequent sections. Free energy value, entropy, chemical equilibrium, spontaneity, and examples will all be discussed.

Difference Between Exergonic and Endergonic Reactions in Tabular form

Parameters Exergonic Reaction Endergonic Reaction
Meaning The exergonic reaction means free energy is being released from the system. The free energy is absorbed in the system as a result of the endergonic reaction.
Relations   Exothermic reactions are related to exergonic reactions. Endothermic reactions are related to endergonic reactions.
Free energy Gibbs's free energy is a positive value. Gibbs's free energy has a negative value.
Products and reactants In an exergonic reaction, the energy of the reactants is higher than that of the products. In an endergonic reaction, the energy of the reactants is lower than that of the products.
Examples The reaction of sodium and chlorine to produce table salt, as well as combustion and chemiluminescence. On the cell membrane, protein synthesis, nerve conduction, muscle contraction, and sodium-potassium exchange occur.
Nature Exergonic reactions are spontaneous. Endergonic reactions are non-spontaneous.

What is an Exergonic Reaction? 

In terms of chemical thermodynamics, the exergonic reaction is defined as a chemical reaction in which the change in free energy is negative. As previously stated, this results in a spontaneous reaction, which means that the reaction occurred without any external input to the system. During this reaction, the system is closed, and the initial and final temperatures are the same. Any reaction that occurs at a constant temperature with any additional external driving force is exergonic, according to the second law of thermodynamics.

The exergonic reactions, as previously stated, are spontaneous in nature but do not occur at any observable rate. The products contain less energy than the reactants because energy is released during the reaction. As a result, the enthalpy change is negative. Enthalpy is the energy stored in bonds in biology, and the change in enthalpy is the difference in bond energies between the products and reactants. It is also the state function used in many measurements, such as those of the chemical, biological, and physical systems at constant pressure. Enthalpy is measured in joules in the International System of Units (SI).

Because of the spontaneous nature of exergonic reactions, they are frequently referred to as irreversible reactions, which means the reactions are ready or eager to occur.

Due to the spontaneous nature of the exergonic reaction, they are often called irreversible reactions, which means the reactions are ready or eager to occur with very few external forces. These reactions liberate more heat and are called "favourable reactions" in the thermodynamics field. Although not all exergonic reactions are self-started, some reactions do require a small amount of external energy, and once the requirement for external energy is fulfilled, the reactions proceed to break the bonds and form new bonds, and energy is released as the reaction takes place. The result is a net gain of energy in the environment and a net loss of energy by the reaction system.

Exergonic reactions include the combustion of sodium when exposed to air, cellular respiration, which is one of the most well-known examples, and the burning of a log, which is another.

What is an Endergonic Reaction?

The endergonic reaction, like the exergonic reaction, is a chemical reaction; the name was derived from the Greek words "endon" (within) and "ergon" (work). The entire phrase defines the absolute nature of the endergonic reaction, namely, that heat is absorbed and an unfavourable reaction takes place. Because the standard changes in free energy are positive, this chemical reaction requires an additional external driving force to complete the reaction.

The reaction is also theoretically explained in layman's terms as the total amount of energy required to complete the reaction is far greater than the energy gained from the reaction. As a result, the endergonic reaction's total useful energy is negative. The reaction will give the positive sign at standard Gibbs free energy in the standard state, that is, at the standard pressure (1 bar) and standard concentrations (1 molar) of all the reagents.

The change in entropy of the system during the reaction determines the type of reaction. Entropy is a key concept in physics and chemistry and is also applied in many other terms, like cosmology and economics. Although our main concern is in physics and chemistry, i.e., in physics, it is a part of thermodynamics, and in chemistry, it is a core concept in physical chemistry. According to the second law of thermodynamics, the entropy of one system decreases when the entropy of another system increases. Hence, they have positive and negative values and are measured by the randomness or disorder of a system.

The initial energy required for the endergonic reaction is called activation energy, which is defined as the minimum amount of energy provided for chemical compounds to perform the reaction. And the activation energy is often larger than the overall energy of the exergonic reaction. Protein synthesis, melting ice into liquid water and mixing baking soda and citric acid in water are all examples of endergonic reactions.

Main Difference Between Exergonic and Endergonic Reactions in Points

  • The primary distinction between exergonic and endergonic reactions is that exergonic reactions occur spontaneously and release energy into the environment. On the other hand, an endergonic reaction is a non-spontaneous reaction in which the energy is absorbed from the surrounding environment.
  • Secondly, Gibbs's free energy would be the most distinct point to differentiate in the reaction. The Gibbs free energy in the exergonic reactions is negative, whereas the same Gibbs free energy is positive in the endergonic reaction.
  • Entropy, as previously stated, is a crucial concept in physics and chemistry. When exergonic reactions occur, the entropy increases, whereas when an endergonic reaction occurs, the entropy decreases.
  • An endergonic reaction frequently requires the triggering of the process by an external driving force. In the case of an endergonic reaction, it does not require any outside energy to begin. However, in rare cases, exergonic reactions may necessitate the application of external force.
  • Endothermic reactions are the thermal manifestation of endergonic reactions, while exothermic reactions are the thermal manifestation of exergonic reactions.
  • The products and reactants are other factors that distinguish the following reactions; in endothermic reactions, the energy of the reactants is lower than that of the products. And in the exergonic reactions, the energy of the reactants is higher than that of the products.
  • If the surrounding temperature is slowly rising, then the reactions are exergonic; if the surrounding temperature is lowering, then the reactions are endergonic.
  • Exergonic reactions are referred to as favourable reactions because they are spontaneous and do not require external energy to occur. And the endergonic reaction is called an unfavourable reaction due to its non-spontaneous nature and the requirement of an external driving force.
  • Examples of exergonic reactions are as follows: glycolysis, fatty acid catabolism, combustion of propane, and so on. Here are some examples of endergonic reactions: photosynthesis, the formation of nitrogen monoxide, electrolysis of water, and so on.

Conclusion

Chemical reactions proceed in both the forward and reverse directions until chemical equilibrium is reached and the forward and reverse reactions proceed at the same rate. At chemical equilibrium, the system is in its most stable energy state.

Before wrapping up the article, it is beneficial to note that one cannot predict how quickly a reaction will occur based on whether it is endergonic or exergonic. Rust formation, for example, is both an exergonic and an endergonic reaction, but it occurs over a long period, so slowly that the release of heat into the environment is easy to detect. Both reactions are coupled in biological systems, so the energy released by one reaction is used by the other.

All the chemical reactions taking place all around us can be classified in either way as an endergonic reaction or an exergonic reaction. To conclude, the two reactions have opposite definitions and properties. An endergonic reaction is referred to as an absorption of energy in the form of work, whereas an exergonic reaction is referred to as a release of energy in the form of work. The primary distinction between endergonic and exergonic reactions is that endergonic reactions are non-spontaneous and unfavourable, whereas exergonic reactions are spontaneous and favourable.

References

  • Endergonic reaction - Wikipedia
  • Exergonic reaction - Wikipedia
  • Difference Between Endergonic and Exergonic | Compare the Difference Between Similar Terms

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