22.21.Show that 1 dyn/cm^2 equals 1 10 ^6 bar.
22.22.Siliconesare polymers of silicon and oxygen chains,
with organic side groups attached to the silicons. They have
many useful properties and are extensively used in society.
Although they have very, very low vapor pressures, they do
have vapor pressures. They also have very low surface energies.
Comment on the potential for silicone’s presence on any real
surface.
22.23.Rationalize the presence of R, the ideal gas law con-
stant, in equation 22.21.
22.24.Atoms on a planar surface have different interatomic
distances depending on the Miller indices of the exposed sur-
face plane. NaCl has a face-centered cubic lattice with a lat-
tice parameter of 5.640 Å. What are the closest Na–Nadis-
tances for a surface made by (a)the (100) plane; (b)the
(110) plane; and (c)the (111) plane?
22.25.Atoms on a planar surface have different interatomic
distances depending on the Miller indices of the exposed
plane. In a cubic crystal, what plane or planes have the atoms
closest together?
22.26.Define the term cleanas applied to solid surfaces. Why
are clean surfaces so difficult to obtain?
22.27.From the (limited) data in Table 22.2, is there a trend
for the relationship between the surface energy of ionic com-
pounds and the magnitudes of the charges on the ions?
22.28.A china cup breaks when the ionic or covalent bonds
are broken due to shock, stress, or some other influence. Even
if such a cup were broken into two simple pieces, just putting
the pieces back together will not make the bonds re-form.
Why? We need things like glue because of this phenomenon.
22.29.Satellites in space often suffer from vacuum welding,
in which two metal parts in contact tend to stick together
more than expected over a period of time. Why does this phe-
nomenon occur in space and not on Earth?
22.30.Calculate the number of gas atoms or molecules per
cubic centimeter at 273 K if the pressure is 1.00 10 ^8 torr.
22.31.If an oil-filled rotary vacuum pump reaches an ulti-
mate vacuum of 1.0 10 ^4 torr, how long does it take a sur-
face exposed to that pressure to build up a monolayer of ad-
sorbed molecules?
22.32.How many langmuirs is exposure to 1.00 bar for one
second equal to? Does the concept of exposure hold at this
magnitude? Why or why not?22.6 Coverage; Catalysis
22.33.Are the following processes examples of homoge-
neous or heterogeneous catalysis? (a)Hydrolysis of immiscible
ethyl acetate () in an aqueous basic solution. (b)Conversion
of NOxgases to N 2 and O 2 by platinum metal. (c)Decom-
position of atmospheric ozone by NO gas. (d)Oxidation of
ethyl alcohol, C 2 H 5 OH, by the enzyme alcohol dehydroge-
nase, ADH, to acetaldehyde in the body. (e)Solid-state con-
version of C (graphite) to C (diamond) by transition metal ad-
ditives at high pressure.
22.34.Derive equation 22.27 from equation 22.26.
22.35.Early attempts to coat metals with Teflon, poly(tetra-
fluoroethylene), resulted in a polymer layer that peeled off the
surface easily. Later attempts gave coatings that were much
more durable. What type of adsorption processes are being
manifested in either situation? What technical problem had to
be solved in order to develop durable coatings?
22.36.At about 450 K, carbon monoxide has the following
coverages on platinum at the given pressures:Coverage Pressure (torr)
0.25 1.5 10 ^8
0.45 7.0 10 ^8
0.65 3.5 10 ^7
0.72 8.7 10 ^7
0.78 1.9 10 ^6
0.82 6.8 10 ^6Show that this data follows a Langmuir isotherm. What is the
equilibrium constant for the adsorption process?
22.37.The individual catalysis steps occurring at a surface leave
out the energy of the desorption of products. Argue that this
step, of necessity, should occur with very little change in energy.Exercises for Chapter 22 791