CHEN 3102 Lecture Notes - Lecture 48: Langmuir Adsorption Model, Rate-Determining Step

• School: UMN
• Department: Chemical Engineering
• Course: CHEN 3102
• Professor: Paul Dauenhauer

Document Summary

Langmuir adsorption isotherm theta is between 0 and 1 consider rxn proceeds on the surface we need to propose some mechanism as to how it works; many possibilities. Mechanism (assume this step is equilibrated, ka = eqbm constant: (this step is rate limiting) we want the rate this is where we can sub in the langmuir isotherm. -> the 1 in the denominator is very large in comparison to the ka[a] term. -> first order behavior: large [a] zero order. When we substitute surface concentrations with the langmuir isotherm, we call this: langmuir-hinshelwood kinetics, hougen-watson kinetics, lhhw. Two classes: all adsorption/desorption steps are equilibrated, and the rate determining step is a surface reaction. Chen3102_reactionsandreactors page 1: all adsorption/desorption steps are equilibrated, and the rate determining step is a surface reaction this is usually how it occurs b/c surface rxn = rate determining step; adsorption/desorption are fast. Surface rxns are fast and the rds is adsorption/desorption.