For the decomposition of substance A in the gas phase at

CHEMISTRY · Multi-part · AP · Chemistry · Kinetics · Kinetics

Problem

450\,\text{K}

, the experimentally determined rate law is

\text{rate} = k\,[A]\,[\text{Cat}]

where

[\text{Cat}]

is the molar concentration of a homogeneous catalyst present in the reaction mixture. A chemist prepares the following experiment: Initial conditions at

t = 0\,\text{s}

[A] = 0.200\,\text{M}

[\text{Cat}] = 0.0100\,\text{M}

Rate constant

k = 2.50 \times 10^{2}\,\text{M}^{-1}\,\text{s}^{-1}

450\,\text{K}

. After

600\,\text{s}

, an impurity introduced with the reactant mixture has poisoned

5.0\%

of the catalyst, rendering that fraction permanently inactive for the reaction. (a) Calculate the initial rate of disappearance of A (in

\text{M}\,\text{s}^{-1}

) at

t = 0\,\text{s}

. (b) Assuming the concentrations of A and active catalyst are still approximately their initial values after

600\,\text{s}

, determine the instantaneous rate at that time. (c) Determine the percentage decrease in the reaction rate that results solely from the catalyst poisoning during the first

600\,\text{s}

. Show your work and state any assumptions clearly. (d) Explain why even a small loss of active catalyst can have a disproportionately large effect on the observed rate for this reaction.

Related theory

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