Open-Sequence Mechanisms Derivation of Rate Law from Mechanism

2 Open-Sequence Mechanisms Derivation of Rate Law from Mechanism 

The derivation of a rate law from a postulated mechanism is a useful application of reaction mechanisms. It shows how the kinetics of the elementary reaction steps are reflected in the kinetics of the overall reaction. The following example illustrates this for a simple, gas-phase reaction involving an open sequence. The derivations typically employ the stationary-state hypothesis (SSH) to eliminate unknown concentrations of reactive intermediates. 

The decomposition of N205 to NO, and 0, is a simple system (if we ignore dimerization of NO, to N204) and a first-order reaction  

If we simply add the three steps, we do not recapture (A). To get around this, we introduce the stoichiometric number, s, for each step, as the number by which that step must be multiplied so that addition of the steps results in (A)  

This set of linear equations can be solved by inspection, or, more formally, by Gauss-Jordan reduction of the augmented coefficient matrix  

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