Introduction:
Chemical reactions are when two or more compounds are involved in creating a new compound or a new set of compounds through a series of changes. These changes might involve energy exchange or utilization of energy in different forms. Endergonic and Exergonic are such chemical reactions where exchange of energy is involved.
Endergonic Versus Exergonic Reactions:

 The word endergonic can be split as endo meaning within while exer in exergonic can be understood as external or outside. As the word depicts endergonic chemical reactions can be defined as reactions that absorb energy from the surrounding environment to complete the reaction while exergonic reactions are ones which release energy in different forms when the reaction is completed. The energy can be released in any form such as heat or light.
 Since energy is taken in during the chemical reaction the resultant products of the endergonic reactions have higher energy content than the reactants though it is the reverse in the exergonic reactions.
 In any chemical reaction the chemical bonds between molecules are broken down. In exergonic reactions the resultant chemical bonds which are formed are stronger than the ones which were broken down while in endergonic reactions the chemical bonds that are formed are weaker when compared to the bonds that were broken initially.
 Exergonic reactions occur spontaneously and are considered as favorable reactions. Endergonic reactions are non spontaneous and are considered as unfavorable reactions. In other words exergonic reactions occur on their own and or not dependant on any source of energy to initiate the reaction which is not the case with endergonic reactions.
 The energy in a molecule is referred to as Gibbs free energy. The difference between the free energy of the products and the free energy of the reactants is called the change in free energy. If the change in free energy is positive this means that energy has been absorbed while a negative change in free energy means that energy is being released in to the surroundings during the course of the chemical reaction. Exergonic reactions have a negative change in free energy while endergonic reactions have a positive change in free energy.
 Cellular respiration in plants is considered as an exergonic reaction where in plants take in sugar and oxygen and convert them into carbon-di oxide and water. Photosynthesis in plants is the reverse and convert carbon-di oxide and water into sugar and oxygen. Burning of a fuel molecule to release energy is also an example of exergonic reactions.
 Exergonic reactions can offer energy for the endergonic reactions while the reverse is not possible.
 An endergonic reaction is often called a reversible reaction. For example, when a wooden log is burned the reactions that formed the log is being reversed and the carbohydrates of the log are broken down into the resultant carbon and water molecules with the help of a small amount of the activation energy in the form of heat. However, the exergonic reaction is not reversible that is to assemble the log again after burning is not possible.

Conclusion:

Chemical reactions can be considered as a system and energy exchange takes place between the system and the surroundings. Such energy exchanges happen as a part of exergonic and endergonic reactions. These two types of chemical reactions can happen inside the body, within living organisms or even within the environment.