IB Chemistry R2.2.7 Energy Profiles and Transition States Key Definitions

A graph showing how the potential energy of a system changes as a reaction progresses from reactants to products. The horizontal axis shows the reaction coordinate; the vertical axis shows potential energy.

An intermediate is a species that is formed in one elementary step and consumed in another. It is not present in the overall reaction equation because it does not appear in the final products or reactants.

The slowest step in the mechanism is called the rate-determining step (RDS).

A measure of the progress of a reaction, used as the horizontal axis of an energy profile. It represents the sequence of bond-breaking and bond-forming events from reactants to products.

A transition state represents the highest-energy arrangement of atoms during an elementary step. It is the point where bonds are partially broken and formed, and the system is at the peak of its energy profile.