Kinetic equations are non-linear

For mechanisms where all steps consist of unimolecular reaction steps, the kinetics of the reaction is available analytically for arbitrarily large mechanisms. However, kinetic 

An inert adsorbate does not have a well defined chemical potential and if inert surface species are present, the model is not soluble without additional assumptions on the behavior of the inert. 

Adsorbed inerts with constant coverage are better described by an adjustment of the number of adsorption sites. Adsorbed inerts with variable coverage are better described as reactants. 

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