Pressure Effects in Gas-Phase Reactions

In the review of Eckert mentioned above, the study of Eckert and Boudart [61] on pressure effects in the decomposition of hydrogen iodide was summarized  

This is one of the few gas phase reactions that seems to occur in the single bi-molecular step as shown and so can be handled directly with Eq. 1.7 I2. 

For gases, the activity can be expressed as the fugacity (with standard state of 1 atm), and so Eq. 1.7-4 shows 

the ratio of the observed rate constant at high to that at low pressures is. 

If the activated complex were not considered, a similar derivation would lead to 

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