Estimation of Chemical Rate Parameters by Conventional Methods

Estimation of Chemical Rate Parameters by Conventional Methods 

The thermodynamic formulation of the transition state theory (TST), as applied to a unimolecular reaction described symbolically by 

From this expression, it is clear that a complex temperature dependency is an expected consequence of the TST analysis. When Ac is small relative to the gas constant R, the following familiar rate expression can be obtained  

It can be shown that the numerical value of the group (kTe/h) in the preceding expression is in the range 10 -10 °s at process temperatures, i.e., temperatures in the range 500-1,500 K. Therefore, unless a unimolecular reaction proceeds through a tight transition state, i.e., AS = 0.0, the pre-exponential factors of these reactions are expected to deviate from this range. 

It is also useful further to classify unimolecular reactions as simple or 

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Vlil. Estimation of Chemical Rate Parameters by Conventional Methods... 

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