Notes on Espenson Method for Determining Catalyzed Reaction Fitting-Constants

Espenson states that many catalyzed reactions can be represented in a unified equation. Based on the basic assumption that the catalyzed reaction occurs in 2 reaction mechanisms (zeroth-order and first-order), he also introduced a time-lag-based equation for determining the fitting-constants, q and κ, using a combination of outset and near-end data. A new method, compiled based on the outset and near-end data separately, has been introduced. This study aims to demonstrate the inaccuracy of Espenson Method. The study was carried out theoretically, and the inaccuracies were tested by applying both methods to the literature data. Assessment is based on the k_obs and κ values. The results showed that Espenson Method does not always use basic assumptions. The average percentage difference in the mean value of k_obs, relative to the new method was 14.24% and for κ was 52.23%. The q value is not constant; q is not the maximum velocity. Doubling [Cat.] will double q, but k_obs and κ are the same. Therefore, q is simply a maximum relative velocity. The real constant is k_obs as the observed catalyst constant.