Page 170 - Basic physical chemistry for the atmospheric sciences

1 5 6 Basic physical chemistry

0
are j = 4 . x 1 0 - 3 s - 1 and k = 2 I .O x l 0 - 2 0 m3 molecule - 1
s - 1 , respective y . Use Eq. (7. 2 3) to calculate the ratio of
l
[N02(g)] to [NO(g)] at 20°C and I atm.
7 . 1 3 . If 1 , n2, n3, and nM are the concentrations of O , 02, 03, and
n
the inert molecule M i n reactions (7.24) to (7.27), write the
n
expressions for dn/dt, dn2/dt, and dn/dt in terms of 1 , n2,
n3, and nM and the four rate coefficients defined by Reac­
tions (7.24) to (7.27).
7. 1 4 . U s ing the expressions for dn1/dt, dnzfdt, and dn3/dt derived
.
in Exercise 7 1 3 , show that n 1 + 2n2 + 3n3 = constant. Could
you have predicted this result?
7 . 1 5 . Write the catalytic cycles and the net reactions correspond­
H
ing to Reaction (7. 28) when X = H and when X = 0 .
7. 1 6 . If the rate coefficient for Reaction (7 .27) i s fitted to the
)
Arrhenius relation (3 .9 , the values of A and Ea are 8 x 1 0 - 1 2
3
cm molecule - 1 s - 1 and 1 7 . I x 1 0 3 J mol - 1 , respectively.

The corresponding values of A and Ea for reaction (7.36b)
3
are 4 . 7 x 1 0 - 1 1 cm molecule - 1 s - 1 and 0.4 x 1 0 3 J mo1 - 1 ,
respectively. Can the rate coefficients for the Reactions
(7.27) and (7.36b) ever be the same? Which is the larger?

Notes
An electron-volt is the energy gained by one electron when it is accelerated through
an electrical p otential difference of 1 volt.
2 The term radical (also called f r ee radical) refers to an atom or molecule containing
an unpaired electron; as might be expected, radicals are very reactive.
3 In 1 99 2 nitric oxide was voted "molecule of the year" by the journal Science. Not
only is it a destroyer of ozone [see Reaction (7.22)), a suspected carcinogen, and a
precursor of acid rain, it is essential to activities in the brain and in the body's
immune system.
4 The percentage increase in DNA damage is about twice the percentage decrease in
the total ozone column. "Total ozone column" is the integrated amount of ozone in a
vertical column of unit horizontal cross-sectional area, extending from the Earth's
surface to the to p of the atmosphere. If all of the ozone in such a column were to be
brought to STP, it would have a depth of only a few millimeters, and most of this
would derive from the stratosphere.
5 In the remainder of this chapter, all of the chemical species are gases unless stated
otherwise. Therefore, for conciseness, we will drop the parenthetical "g," indicating
gas following the chemical symbol.
6 This account is based in p art on a very readable discussion of this topic given in
(
Chemistry o f Atmospheres by Richard P. Wayne, Oxford University Press 1 991), to
which the reader is referred for more detailed infonnation and original references.
7 The symmetric form of chlorine dioxide (OCIO) is different from the unstable species
CIOO in Reaction (7.42b). However, the presence of OClO p rovides an important
indication of the amount of CIO and therefore the destruction of odd oxygen in the
ozone hole.