A Series of Irreversible Steps - General Approach

One relatively common sequence of elementary steps is that consisting of two or more irreversible steps. One example of a more complicated unimolecular reaction demonstrating this behavior is provided in Illustration 7.5. 

One of the easiest catalytic reforming reactions methylcyclohexane (MCH) to toluene (TOL)  

Note that this method of writing reactions without incorporating the active site, which has been frequently used in the past, can be ambiguous and create difficulties. To conform to the approach adopted in this book, this sequence should be written invoking an active site,, as  

the probability of losing 6 H atoms and forming 3 H2 molecules in a single elementary step is essentially zero, thus one already can see that a modification is almost certainly needed. We will address this complication a little later. Ignoring this concern for now, if the sequence of step 4-6 is used along with the assumption that MCH is the MARI, then a = Lk Kmch and b = Kmch, and Arrhenius plots of these two parameters give values of E — 33kcal mole for k, while AH°h = 30 kcal mole and AS°j = -45 

Commensurate with this additional information, the assumption of a RDS was discarded and the following sequence of irreversible steps was proposed [32]  

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