过渡状态

Background to Know

In chemical reactions, the focus is usually on the reactants and products, but there's a lot more going on in-between these two points. For a reaction to occur a specific amount of energy needs to be put in to the reactants. This amount of energy is known as activation energy ($E_a$).

What is a Transition State?

At the highest point of the activation energy ($E_a$) is the transition state. The transition state describes the arrangement of atoms at the highest energy during the reaction. For a reaction to reach the transition state the increase in energy comes from the collision of molecules. When molecules collide, this can change how they were originally arranged. If the atoms can gain enough energy to reach the transition state, they are always converted to products according to the transition state theory or activated complex theory. This is why the transition state is also known as the activated complex.

The transition state can be thought of as an intermediate between reactants and products: $$A\ +\ BC\ \rightarrow\ A---B---C\ \rightarrow\ AB\ +\ C$$ **Catalysts **can be used to stabilize the transition state, they do this by lowering the activation energy of a reaction.