13.6 Experimental Molecular Study of Chemical Reaction Mechanisms 615
PROBLEMS
Section 13.6: Experimental Molecular Study of Chemical
Reaction Mechanisms
13.37For a velocity selector such as depicted in Figure 13.21,
find the molecular speed selected if the distance
between the rotating disks is 2.00 cm, the difference
in orientation of the two disks is 15.0 degrees, and
the rotational speed is 82100 revolutions per
minute.
13.38For the data in the previous problem, find the range of
speeds selected if the slots in the disks have a width of
2.00 degrees.
13.39For the data in the two previous problems, find the width
of slots necessary to give a range of speeds equal
to 20.0 m s−^1.
13.40Find the value of the forward rate constant of the reaction
of Eq. (13.6-4) for 298 K and for 373 K. Express your
results in cm^3 molecule−^1 s−^1 and in L mol−^1 s−^1.Summary of the Chapter
Catalysis involves an alternative mechanism in which the catalyst is involved. Cataly-
sis is divided into three classes: heterogeneous catalysis, homogeneous catalysis, and
enzyme catalysis. Heterogeneous catalysis at the surfaces of solids involves adsorption
of the reactants. We discussed the Langmuir theory of adsorption and applied it to
heterogeneous catalysis. Homogeneous catalysis involves mechanisms with steps that
occur in a single phase, and example reactions were analyzed.
The accepted theory of biological catalysis asserts that an enzyme possesses an
active site into which the reactant molecule fits in such a way that it is more reactive
in the active site than out of it. We obtained the rate law for the simplest mechanism,
due to Michaelis and Menten.
We discussed several special topics in reaction mechanisms: Autocatalytic reac-
tions and oscillatory reactions were discussed, as was the reaction kinetics of polymer
formation and the kinetics of nonequilibrium electrochemistry.
We discussed various techniques for direct detection of reaction intermediates.
These techniques included direct observation of the reaction intermediates and study
of their effects. A survey of work on the gas-phase chemical reaction was presented:F+H 2 −→H+HFAlthough this reaction has been extensively studied on the molecular level, both exper-
imentally and theoretically, it is still the subject of ongoing research and cannot be said
to be completely understood.ADDITIONAL PROBLEMS
13.41Label each statement as either true or false. If a statement
is true only under special circumstances, label it as false.
a.A catalyst can change the equilibrium constant of a
reaction.
b.A reaction can be catalyzed heterogeneously if only
one of the reactants is adsorbed.
c.An inhibitor for an enzyme-catalyzed reaction must
compete with a reactant for an active site.
d.If a catalyst catalyzes a forward reaction, it must also
catalyze the reverse reaction.
e.One way to verify a reaction mechanism is to observe
the presence of reactive intermediates.