Project ForgeChemical Reaction Engineering
Reaction Kinetics
GATE 2016
Hard
A porous pellet has Pt catalyzing a reaction, either (1) throughout the pores or (2) only near the external surface. At a LARGE Thiele modulus, which statement is TRUE?
- ASince the reaction rate is much greater than the diffusion rate, Scenario 1 occurs
- Since the reaction rate is much greater than the diffusion rate, Scenario 2 occurs
- CSince the reaction rate is much lower than the diffusion rate, Scenario 1 occurs
- DSince the reaction rate is much lower than the diffusion rate, Scenario 2 occurs
Explanation
A large Thiele modulus means the intrinsic reaction rate greatly exceeds the diffusion rate through the pores, so reactant is consumed near the external surface before penetrating deep pores — the pellet effectively behaves as if catalyst were placed only near the surface (Scenario 2), regardless of whether it's actually distributed throughout.
Source: GATE CH 2016 (2016)
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