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Activation energy or activation energy of a reaction is one of the most important concepts which has a lot of application when we talk of the enzyme chemistry of the human body. However, it is something related to every chemical reaction, and it is the energy required by a specific substrate to react with the other to form a product. When we talk about the concept of catalysts in a chemical reaction, activation energy has a lot to do with it.
The activation energy in detail
Why would an energy-releasing reaction with a negative ∆G need the energy to proceed? To learn the concept, let us explore what reactant molecules go through at the time of a chemical reaction. To perform a reaction, all or a few reactant’s chemical bonds are to be segregated so new product bonds can form. To bring that state of bonds where they easily break, the molecule needs to be bent, making it unstable. This state is known as its transition state. A transition state is moreover a high-energy form of the molecules, where some amount of energy called – the activation energy – must be provided so as for the molecule to reach it. Because the transition state is not stable, the reactant molecules will not stay long but will quickly go to the other step of the given chemical reaction.
In general, the transition state of a reaction is always at a higher energy level than the reactants or products, such that EA always has a positive value – regardless of the reaction being exergonic or endergonic. The activation energy shown in the graph below is for the forward reaction (reactants – products), which is exergonic. If the reaction were to proceed in the reverse direction (endergonic), the transition state would remain the same, but the activation energy would be larger. This is because the product molecules are of lower energy and would thus need more energy added to reach the transition state at the top of the reaction “hill.”
The source of the activation energy is mainly heating, with reactant molecules absorbing thermal energy from their surroundings. The thermal energy increases the speed of the reactant molecules’ motion. It results in increased force and frequency of collisions. Further, it also pushes the bonds and atoms into separate molecules. Hence, it supports the breakage of bonds. Once a special reactant molecule soaks in enough energy to reach a transition state, further, it can go forward through the rest of the reaction.
Activation energy graph
Activation energy and a reaction rate
The entire activation energy given to a chemical reaction is related to its rate. The presence of more activation energy slows down the chemical reaction. It happens because molecules finish the reaction only after reaching the peak of the barrier of activation energy. As the barrier gets high, fewer molecules will get the required energy to cross at a given moment and time.
Many of the given reactions have such a rate of high activation energies that they often don’t go forward at all, even at a little amount of energy. (To be clear, this is a good thing – it wouldn’t be so great if propane canisters spontaneously combusted on the shelf!) Once a spark has provided enough energy to make the molecules reach over the barrier of activation energy, these molecules release the energy after completing the reaction. The energy thus released helps different fuel molecules to get over the required energy barrier which will ultimately lead to a chain reaction.
The activation energy tends to be highly elevated. Hence, it creates an issue where it gets challenging to proceed with the reactions at the surrounding temperature. Fortunately, it is feasible to reduce a reaction’s activation energy and thus enhance its pace. Catalysis is the process of accelerating a reaction by lowering its activation energy, and the factor that is introduced to decrease the activation energy is termed a catalyst. Biological catalysts are known as enzymes, and we’ll examine them in detail in the next article.
Conclusion
In this article, we studied various elements related to activation energy. Activation energy is nothing but the minimal additional energy required by two reacting molecules to produce a product. The energy is the bare minimum that can excite the particles to produce the result.
