Problems with AP Chemistry: Catalysts and Rates/Mechanisms?

Posted on 2015-10-13 06:45:00 in Chemistry by

Hey guys! I have two questions that I'm stuck on.

1.) Platinum nanoparticles of diameter ~2 nm are important catalysts
in carbon monoxide oxidation to carbon dioxide.
Platinum crystallizes in a face-centered cubic arrangement
with an edge length of 3.924 Å. (a) Estimate how many platinum
atoms would fit into a 2.0-nm sphere; the volume of a
sphere is

. (b) Estimate how many platinum atoms
are on the surface of a 2.0-nm Pt sphere, using the surface area
of a sphere and assuming that the “footprint” of one Pt
atom can be estimated from its atomic diameter of 2.8 Å.

(c) Using your results from (a) and (b), calculate the percentage
of Pt atoms that are on the surface of a 2.0-nm nanoparticle.
(d) Repeat these calculations for a 5.0-nm platinum nanoparticle.
(e) Which size of nanoparticle would you expect to be more catalytically active and why?

2.) The enzyme carbonic anhydrase catalyzes the reaction CO2(g) +
H2O(l) HCO3-(aq) + H+(aq). In water, without the enzyme,the reaction proceeds with a rate constant of 0.039 s^-1
at 25 C. In the presence of the enzyme in water, the reaction proceeds with a rate constant of at 25 C. Assuming the collision factor is the same for both situations,calculate the difference in activation energies for the uncatalyzed
versus enzyme-catalyzed reaction.

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