Definition of a Reaction Intermediate
A reaction intermediate is a short-lived, transient species that is produced in one step of a multi-step chemical reaction and subsequently consumed in a later step. Crucially, it does not appear in the overall balanced chemical equation.
Key Characteristics and Role
Intermediates are typically unstable and highly reactive, existing for a very brief period before undergoing further transformation. They play a vital role by providing alternative pathways with lower activation energies, enabling the conversion of initial reactants into final products.
Practical Example of an Intermediate
Consider the decomposition of ozone (2O₃ → 3O₂). This reaction can occur in two steps: 1) O₃ → O₂ + O (slow) and 2) O + O₃ → 2O₂ (fast). In this mechanism, the free oxygen atom (O) is a reaction intermediate because it is formed in the first step and then consumed in the second step, thus not appearing in the final equation.
Importance in Understanding Reaction Mechanisms
Identifying and understanding reaction intermediates is essential for elucidating the precise, step-by-step pathway (mechanism) of a chemical reaction. This knowledge helps chemists predict reaction rates, explain observed kinetics, and design more efficient chemical processes by targeting or manipulating these transient species.