AS and Pre-exponential A Factors

Problem 4.14 showed that the observed A factor can be correlated with A S, and more importantly that p and exp(+AS /f ) are related. Consideration of factors contributing to A 5 gave considerable insight into the properties of the activated complex and the process of forming the activated complex for gas phase reactions. Such considerations have proved even more fruitful for reactions in solution. 

Remember, when discussing microscopic quantities appearing in theoretical treatments, molecular units are generally used, e.g. k, the Boltzmann constant. In contrast, when discussing experimental quantities, molar units are generally used e.g. R, the gas constant, is used rather than the Boltzmann constant see Section 7.3, especially 7.3.1 and 7.3.3. 

Answer. The thermodynamic formulation of transition state theory (Section 4.4 and Equations (4.39) and (4.40)) is 

A plot of loge k/T versus 1 IT should have slope = —AH /R 

The intercept cannot be found by extrapolation (scale trouble, see comment below), and must be found by calculation. 

---