The main difference between exergonic and endergonic reaction is that exergonic reaction is spontaneous reaction whereas endergonic reaction is a non-spontaneous reaction
Exergonic Reaction vs. Endergonic Reaction
Exergonic is a favorable chemical reaction that has a negative Gibbs free energy. It indicates that an exergonic reaction is a spontaneous reaction since in this reaction Gibbs energy has a negative value. In such type of reactions, energy is liberated into the surrounding, so products have a lower amount of energy than that of the reactants. Due to this reason, change in enthalpy has a negative value for an exergonic reaction. Entropy increases in this reaction because of the disorder of the system. Exothermic reactions are also included in exergonic reactions. While in contrast, the endergonic reaction is a type of reaction in which Gibbs free energy has a positive value. A nonspontaneous reaction is also termed as an unfavorable reaction. In such type of reaction, energy must be provided from the outside of the reaction for progression. This is the reason products get a higher value of energy than reactants. Change in enthalpy has a positive value. Since new products are formed, the entropy of the system decreases. Endothermic reactions are also included in endergonic reactions.
Exergonic reactions can also be termed as catabolism (destructive part of metabolism) when complex molecules are broken down whereas endergonic reactions can also be termed as anabolism (creative part of metabolism) when new complex molecules are build up from simple molecules.
What is Exergonic Reaction?
Gibbs free energy is a thermodynamic potential which is used to identify whether a reaction is spontaneous or non-spontaneous. A negative value of Gibbs free energy shows the reaction is spontaneous and a positive value shows that the reaction is non-spontaneous. The exergonic reaction is an irreversible reaction which occurs spontaneously in nature. It means it is ready or eager to occur with very little external stimuli. Example of such reaction is the combustion of sodium when exposed to oxygen present in the air. Burning of a log is another example of an exergonic reaction. These reactions liberate more heat and are called favorable reactions in thermodynamic field. The Gibbs free energy is negative under constant pressure and temperature which means that more energy is liberated rather than absorbed. Cellular respiration is a classic example of it. Almost 3012 kJ energy has released when one molecule of glucose is converted to carbon dioxide. This energy is used by the organisms for other cellular activities. All catabolic reactions, for example, carbohydrate, fat and protein break down liberates energy for the living organisms to do work. Some exergonic reactions do not happen spontaneously and need a small amount of energy to start the reaction. Once this energy requirement is fulfilled by an outside source, the reaction proceeds to break the bonds and form new bonds and energy is released as the reaction takes place. This results in a net gain of energy in the environment and a net loss of energy by reaction system.
What is Endergonic Reaction?
There are many chemical reactions which happen only when a sufficient amount of energy has supplied from the surrounding. On its own, these reactions cannot occur. External energy aids to break these bonds. The energy released from the breaking down of the bonds that keeps the reaction going. This energy is not enough to sustain the reaction, and external energy is needed. These reactions are called endergonic reactions. Protein synthesis is an anabolic reaction which needs small amino acids to come together to form a protein molecule. It involves a lot of energy to make the peptide bonds. Sodium-potassium pump in the cell membrane is involved in the pumping out of sodium ions and movement of potassium ions against the concentration gradient to allow call depolarization and nerve conduction. This movement against gradient needs a lot of energy which comes from the breakdown of ATP molecule. Similarly, muscle contraction can happen only when existing bonds between actin and myosin fibers break to make new bonds. This also requires a large amount of energy. Photosynthesis in plants is another example of an endergonic reaction. The leaf has glucose and water, but it cannot generate food. Sunlight is the external source of energy which starts it.
- The exergonic reaction is a spontaneous reaction whereas endergonic reaction is a non-spontaneous reaction.
- The exergonic reaction does not need energy for happening whereas endergonic reaction needs energy.
- In exergonic reaction, energy is liberated into the surroundings whereas in endergonic reaction energy is absorbed from the surroundings.
- In exergonic reaction, bonds which are formed are stronger than the bonds which are broken whereas in endergonic reaction the bonds which are formed are weaker than the bonds which are broken.
- In exergonic reaction, the free energy of the system decreases whereas, in endergonic reaction, the free energy of the system increases.
- In exergonic reaction, change in entropy increases whereas in endergonic reaction change in entropy decreases.
- In exergonic reaction, Gibb’s free energy is a negative value whereas, in endergonic reaction, the Gibbs free energy is a positive value.
It has been concluded from the above discussion, all chemical reactions can be characterized as exergonic or endergonic reactions, but both have opposite properties.