In this video, we're going to begin our lesson on the enzyme activation energy. The activation energy, sometimes called the energy of activation, is commonly abbreviated as EA. The activation energy or energy of activation (EA) is defined as the difference in energy between the reactants of a reaction and the transition state of a reaction. We'll define the transition state shortly. Focusing on the activation energy (EA), it represents the minimum amount of energy required to start a chemical reaction. All reactions have an activation energy, and that includes both exergonic and endergonic reactions. The higher the energy of activation is, the slower the reaction will be. The energy of activation dictates the speed at which the reaction will occur: the higher the reaction energy of activation, the slower the reaction; the lower the energy of activation, the faster the reaction will take place.
The transition state is defined as a temporary state of maximum energy within a reaction. Let's take a look at our image below to clarify some of this. Notice that we're showing you this graph where on the y-axis we have the free energy and on the x-axis we have the reaction progress, or the time as the reaction proceeds. We start off with some reactants that have higher free energy than the products, which have lower free energy, making this an exergonic reaction. The transition state is a temporary state of maximum energy in a reaction. At the peak of this curve, we find the transition state. The activation energy, recall, is defined as the difference in energy between the reactants and the transition state. The difference in energy between the two is represented by this region, the activation energy, shown by this yellow bar. The activation energy (EA) represents the minimum amount of energy required to start the chemical reaction. Even in an exergonic reaction, there is a minimum amount of energy that needs to be overcome for the reaction to proceed. This illustrates how the activation energy is represented by the difference in energy between the transition state and the reactants, and how it determines the speed of the reaction.
Now that we've introduced the activation energy (EA), in our next video, we'll talk about how enzymes affect the activation energy. So I'll see you all in that video.