The key difference between endergonic and exergonic is that endergonic reactions are non-spontaneous and unfavourable, whereas exergonic reactions are spontaneous and favourable.
Energy is the capacity to do work. In a system, energy can do work and energy can be changed to other forms such as heat, sound, light etc. When the energy of a system changes as a result of a temperature difference between the system and the surrounding, we say that energy has been transferred as heat. A chemical reaction can be considered as a system. A chemical reaction is a process where one or more compounds are converted into a new set of compounds through a series of changes.
When the reaction proceeds, there can be an energy transfer from surrounding to the system or vice versa. Some of these reactions are spontaneous, and some are not. All the reactions happening in the environment are not spontaneous, but we see these non-spontaneous reactions take place naturally. That is because non-spontaneous reactions are coupled with the spontaneous reactions and they are driven by the energy of the spontaneous reactions.
CONTENTS
1. Overview and Key Difference
2. What is Endergonic
3. What is Exergonic
4. Side by Side Comparison – Endergonic vs Exergonic in Tabular Form
5. Summary
What is Endergonic?
The word “ender” is derived from the word “endo” which means “within”. Therefore, endergonic means absorbing energy in the form of work. Therefore, in an endergonic reaction, the surrounding supplies energy into the system. Furthermore, the products will have higher energy than the reactants. An endergonic reaction is considered to be nonspontaneous or unfavourable. If this energy transfer takes place at constant pressure and temperature, the standard Gibbs free energy will be positive. Thus, the equilibrium constant for an endergonic reaction is less than one.
Photosynthesis is an endergonic reaction which takes places in the natural environment. For photosynthesis, energy is supplied by sunlight. In the human body, when endergonic reactions are taking place, the energy is supplied by the ATP. Hence, endergonic reactions are coupled with ATP hydrolysis reactions.
What is Exergonic?
Exergonic means releasing energy in the form of work. In these reactions, energy is released from the system to the outside. Exergonic reactions are favourable and spontaneous.
Since the energy is released during the reaction, the products contain less energy than the reactants. Therefore, the enthalpy change (∆H) becomes negative. Moreover, if the transfer is carried out at constant pressure and temperature, standard Gibbs free energy will be a negative value.
What is the Difference Between Endergonic and Exergonic?
Endergonic means absorbing energy in the form of work whereas exergonic means releasing energy in the form of work. The key difference between endergonic and exergonic is that endergonic reactions are non-spontaneous and unfavourable, whereas exergonic reactions are spontaneous and favourable. The standard Gibbs free energy will be positive in endergonic reactions, in contrast to exergonic reactions. In exergonic reactions, the products contain less energy than the reactants but, in endergonic reactions, products contain higher energy than the reactants.
Summary – Endergonic vs Exergonic
Endergonic means absorbing energy in the form of work whereas exergonic means releasing energy in the form of work. The key difference between endergonic and exergonic is that endergonic reactions are non-spontaneous and unfavourable, whereas exergonic reactions are spontaneous and favourable.
Image Courtesy:
1. “Endergonic” By J3hoang – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Exergonic” By J3hoang – Own work (CC BY-SA 3.0) via Commons Wikimedia