Reaction Energy Profile

A reaction energy profile, also known as an energy level diagram, is used to illustrate the progress of a reaction in terms of energy.
It typically shows the energy of the reactants, the products, and the activation energy of the reaction.
The horizontal axis represents the progress of the reaction, while the vertical axis represents the energy.
The curve on the diagram shows how the energy of the system changes as the reaction progresses.

Reaction Progress

The reactants are typically at a higher energy level compared to the products in an exothermic reaction. This indicates that energy is released during the reaction.
Conversely, in an endothermic reaction, the products are at a higher energy level compared to the reactants, meaning energy is absorbed during the reaction.

The activation energy is represented by the height of the energy barrier that must be overcome for a reaction to occur.
It’s the minimum amount of energy needed to initiate a chemical reaction.
It’s often represented by the difference in energy between the reactants and the highest point on the energy profile.

A catalyst offers an alternative reaction pathway with a lower activation energy.
This is shown on the reaction energy profile by a curve with a lower energy barrier.
As a result, a catalyst increases the rate of a reaction by allowing more of the reactant molecules to have enough energy to overcome the lower energy barrier.

The top of the energy barrier on a reaction energy profile represents the transition state or activated complex - an unstable arrangement of atoms at the peak of the activation energy barrier.
The transition state represents an intermediate state of the reactants as they are converting into products.
The transition state is often represented on a reaction energy profile by the highest point on the curve.