244e Rate Laws for Reactions with Parallel Pathways: Use of the Electrical Analogy

Ravindra Datta1, Saurabh Vilekar2, and Ilie Fishtik2. (1) Chemical Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, (2) Chemial Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609

The conventional kinetic analysis of the rate law of an overall reaction is limited to a single sequential pathway comprising of a series of consecutive molecular steps that transform the reactants into products. The general approach is based on the time-honored quasi-steady state approximation (QSSA), leading, e.g., to the Temkin relation for the general case. More limiting approaches include the rate-limiting step (RLS), along with the quasi-equilibrium hypothesis (QEH), i.e., the Langmuir-Hinshelwood-Hougen-Watson (LHHW) algorithm. The electrical analogy of the network comprising a sequence of resistors representing the elementary steps is often utilized in this regard in visualizing a RLS. Here we describe a topological approach based on the analogy between reaction-route (RR) graphs described by us earlier and electrical circuits that extends such QSSA analysis to the case of systems involving parallel pathways, and is amenable to RLS/QEH analysis as well. It is illustrated here for the simple case of gas-phase hydrogen-bromine reaction, but is useful for catalytic and enzymatic reactions networks as well.