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Transition State

From our earlier discussions, we know that exothermic reactions release energy and endothermic reactions consume energy. Here, we will plot the potential energy diagrams of exothermic and endothermic reactions. Before we do that, we will discuss the concept of transition state. Consider the hypothetical reaction shown below:

image\Ch 11 Section C first graphic.png

Can you say what type of reaction this is? It is an exothermic reaction. For reactions to proceed, there should be breaking of bonds and formation of bonds. For many reactions, the stability barrier that originally made the reactant molecules stable should be overcome. This is achieved by the formation of an energy-state that has higher energy than the reactants and the products. This high-energy state is often referred as transition state. These transition states have a relatively short life span, and once this highly unstable transition state is formed, it quickly disintegrates to form the products. For a reaction to reach this transition energy level, a certain amount of energy is required. This energy is called the activation energy or the energy of activation.

In the diagram (Figure 11-1), the activation energy depicted in both Figures (a) and (b) are for the forward reactions.

image\Ch 11 fig 11-1a.png


image\Ch 11 fig 11-1b.png

Figure 11-1

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