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How does transition-state theory explain the rate of an elementary chemical reaction?

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A graph showing a potential energy curve for a chemical reaction, with the y-axis labeled potential energy and the x-axis labeled progress of reaction. The curve rises from the initial state (reactants) to a peak labeled transition state (activated complex), indicating activation energy, then drops to the final state (products). — chemical kinetics In the Arrhenius equation, the activation energy (E) represents the minimum amount of energy required to transform reactants into products in a chemical reaction. On a potential energy curve, the value of the activation energy is equivalent to the difference in potential energy between particles in an intermediate configuration (known as the activated complex, or transition state) and particles of reactants in their initial state. The activation energy thus can be visualized as a barrier that must be overcome by reactants before products can be formed.

Transition-state theory explains the rate of an elementary chemical reaction by modeling it as a continuous change in the relative positions and potential energies of atoms and molecules.1

As reactants progress toward products, they must pass through an intermediate configuration known as the activated complex (or transition state), which corresponds to the maximum potential energy along the reaction path. The difference between the energy of this state and the initial state is related to the activation energy, representing the minimum energy required for the transformation to occur.213

The theory assumes that these activated complexes exist in a state of equilibrium with the reactants. Consequently, the reaction rate is determined by two factors:21
* The concentration of the activated complexes, which can be expressed in terms of reactant concentrations.21
* The frequency with which these complexes convert into products.21

By applying statistical-mechanical or thermodynamic principles, the rate constant can be calculated based on molecular dimensions, atomic masses, and interatomic forces.1