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Unformatted text preview: expression for the overall reac)on rate in terms of the adsorp;on equilibrium constants and the rate constant for the surface reac;ons. (II) Show that if the gas phase H2 concentra;on is much greater than the gas phase C2H4 and C2H6 concentra;ons and the adsorp;on equilibrium constants are sufficiently small that the total frac;onal surface coverage is small (much less than 1), then the reac;on will be first order in the C2H4 concentra;on and independent of the other species concentra;ons. Multiple-Component Adsorption with Surface Reaction
species C2H4, H2 adsorp;on species desorp;on (Cn Hm )ad Assump;ons: (i) Each adsorp;on site is equally probable (ii) Heats of adsorp;on depend on species If the hydrogena;on step (reac;on 3) is rate limi;ng, then the overall reac)on rate r is determined by this rate limi;ng step. Thus rate of producIon: rate of reacIon: R(C2 H4 )ad = r = r3 = k3 CC2 H4 CH R(C2 H4 )ad = k3 CC2 H4 CH Since the first surface reac;on (step 3) is rate limi;ng, we need not worry about reac;on step 4 Consider a daily commute to work of 10km by car Concept of Rate LimiIng Step total time = 7.5 min V = 80 km/hr 10 km No suppose one week there is construc;on on the road V = 80 km/hr total time = 28.5 min Road construc;on 4 km maximum speed 10km/h...
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This document was uploaded on 03/14/2014.
- Winter '14