If you breakdown individual reactions at the molecular level you get detailed chemical reactions. The reactions may occur sequentially or parallel. They may occur in different zones (eg. near wall) or different temperatures. The reactions maybe classified as - chain initiating - produce intermediates - chain branching - increase number of intermediates - chain propagating - sustain number of intermediates - chain terminating - consume the intermediates and produce product How do we get a global reaction rate based on reactant concentration through the intermediates? ## 1. Steady State approximation [[Steady State Approximation]] ## 2. Partial Equilibrium Approximation [[Partial Equilibrium Approximation]]