Deducing a Rate Law from the Experimental Data

Assuming that the reaction is essentially irreversible which is reasonable after comparing runs 3 and 5), we ask what qualitative conclusions can be drawn from the data about the dependence of the rate of disappearance of toluene, —rj, on the partial pressures of toluene, hydrogen, methane, and benzene. 

Dependence on the product methane. If methane were adsorbed on the surface, the partial pressure of methane would appear in the denominator of the rate expression and the rate would vary inversely with methane concentration  

However, from runs t and 2 we observe that a fourfoid increase in the pressure of methane has little effect on -r. Consequently, we assume that methane is either very weakly adsorbed (i.e., ) 

Dependence on the product benzene. In runs 3 and 4, we observe that, for fixed concentrations (partial pressures) of hydrogen and toluene, the rate decreases with increasing concentration of benzene. A rate expression in which the benzene partial pressure appears in the denominator could explain this dependency  

The type of dependence of — on Pg given by Equation (10-68) suggests that benzene is adsorbed on the clinoptilolite surface. 

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