1038 CHAPTER 26: Nuclear Chemistry
for^1407 N, 4.00260 amu for^42 He, 1.007825 amu for^11 H, and
16.99913 amu for^1708 O. (b) Calculate the energy change of
this reaction in kJ/mol.
*75.A proposed series of reactions (known as the carbon–
nitrogen cycle) that could be important in the very hottest
region of the interior of the sun is(^12) C (^1) H88nA
A88nB^01 e
B^1 H88nC
C^1 H88nD
D88nE^01 e
E^1 H88n^12 CF
Identify the species labeled A–F.
76.The ultimate stable product of^238 U decay is^206 Pb. A cer-
tain sample of pitchblende ore was found to contain^238 U
and^206 Pb in the ratio 67.8 atoms^238 U32.2 atoms^206 Pb.
Assuming that all the^206 Pb arose from uranium decay, and
that no U or Pb has been lost by weathering, how old is
the rock? The half-life of^238 U is 4.51 109 years.
77.Potassium-40 decays to^40 Ar with a half-life of 1.3 109
years. What is the age of a lunar rock sample that contains
these isotopes in the ratio 33.4 atoms^40 K66.6 atoms^40 Ar?
Assume that no argon was originally in the sample and that
none has been lost by weathering.
CONCEPTUAL EXERCISES
78.Both nuclear and conventional power plants produce
wastes to which the environment is sensitive. Discuss these
wastes and the current problems created by the wastes.
79.If the earth is 4.5 109 years old and the amount of
radioactivity in a sample becomes smaller with time, how
is it possible for there to be any radioactive elements left
on earth that have half-lives of less than a few million years?
BUILDING YOUR KNOWLEDGE
80.Show by calculation which reaction produces the larger
amount of energy per atomic mass unit of material react-
ing.
fission:^235092 U^10 n88n^9440 Zr^140058 Ce 6 10 e 2 10 n
fusion: 2^21 H88n^31 H^11 H
The atomic masses are 235.0439 amu for^235092 U; 93.9061
amu for^9440 Zr; 139.9053 amu for^140058 Ce; 3.01605 amu for
3
1 H; 1.007825 amu for
1
1 H; 2.0140 amu for
2
1 H.
81.What would be the volume of helium, measured at STP,
generated from the decay of the^8 Be sample in Exercise
56?