Active Intermediates and Nonelementary Rate Laws

The rate law could also have concentration terms in both the numerator and denominator such as the formation of HBr from hydrogen and bromine 

Rate laws of this form usually involve a number of elementary reactions and at least one active Intermediate. An active intennediate is a high-energy molecule that reacts virtually as fast as it is formed. As a result, it is present in very small concentrations. Active intermediates (e.g.. A ) can be formed by collision or interaction with other molecules. 

The idea of an active intennediate was first postulated in 1922 by F. A. Ltndemann- who used it to explain changes in reaction or r with changes in 

In the theory of active intermediates, decomposition of the intermediate does not occur instantaneously after internal activation of the molecule rather, there is a time lag, although infinitesimally small, during which the species remains activated. Zewail s work was the first definitive proof of a gas-phase active intermediate that exists for an infinitesimally short lime. Because a reactive intermediate reacts virtually as fast as it is formed, the net rate of formation of an active intermediate (e.g.. A ) is zero, i.e.. 

This condition is also referred to as the P.seudo-Steady-State Hypotheais (PSSH). If the active intermediate appears in n reactions, then 

In Chapter 3 a number of simple power law models, that is, 

Reaction Mechanisms, Pathways. Bioreaciions, and Bioreactors Qtap. 7 

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Sec. 7.1 Active Intermediates and Nonelementary Rate Laws Example 7-2 FSSH Applied to Thermal Cracking of Ethane... 

Section 9.1 Active Intermediates and Nonelementary Rate Laws... 

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