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PAGE 71
ANSWERS TO
ENDOFCHAPTER QUESTIONS
CHAPTER 7: THE FIRES OF NUCLEAR FISSION
Emphasizing Essentials
1
.
Give two ways in which an atom of carbon can differ from another atom of carbon. Then give
three ways in which
all
carbon atoms differ from
all
uranium atoms.
Answer:
One carbon atom can differ from another in the number of neutrons (such as C12 and C13)
and in the number of electrons (we won’t be studying carbon ions, but these do exist). All
carbon atoms differ from all uranium atoms in their number of p, n and e and also in their
chemical properties.
2
. Representations such as
14
N or
15
N give more information than simply the atomic symbol N.
Explain.
Answer:
The symbol N represents the element nitrogen and stands for the naturally occurring mixture of
all isotopes. The symbols
14
N and
15
N represent very specific isotopes with mass numbers of
14 and of 15, respectively.
3
.
a.
How many protons does an atom of
94
239
Pu contain?
b.
What element contains one more proton than uranium? Two more?
c.
How many protons does radon222 contain?
Answer:
a.
94 protons
b.
Np (neptunium), Pu (plutonium)
c.
86 protons
4
.
Determine the number of protons and neutrons in each of these nuclei.
a.
C14 (radioactive)
b.
C12 (stable)
c.
H3 (tritium, a radioisotope of hydrogen)
d.
Tc99 (a radioisotope used in medicine)
Answer:
a.
C14 has 6 protons and 8 neutrons
b.
C12 has 6 protons and 6 neutrons
c.
H3 has 1 proton and 2 neutrons
d.
Tc99 has 43 protons and 56 neutrons
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5
.
E
=
mc
2
is one of the most famous equations of the 20th century. What do the symbols in the
equation represent?
Answer:
E
represents energy,
m
represents mass lost in a nuclear transformation, and c represents the
speed of light.
6
.
Give an example of a nuclear equation and of a chemical equation. In what ways are the two
equations alike? Different?
Answer:
Nuclear equation:
Chemical equation: CH
4
+ 2 O
2
→
CO
2
+ 2 H
2
O
In a chemical equation, the elements do not change their identities in the process of being
converted from reactants to products. Even though they are combined differently, the same
number of atoms of each kind must appear on both sides of the equation. Usually only the
symbols for the elements are given, not their atomic or mass numbers. In a nuclear equation,
the identity of the elements may change, or at least the mass number may change. The values
for both the atomic and mass numbers are often included.
7
.
This nuclear equation represents a plutonium target being hit by an alpha particle. Show that
the sum of the subscripts on the left is equal to the sum of the subscripts on the right. Then do
the same for the superscripts.
Answer:
Subscripts: 94 + 2 = 96 on the left, 96 + 0 = 96 on the right
Superscripts: 239 + 4 = 243 on the left; 242+1=243 on the right
8
.
For the nuclear equation shown in the previous question,
a.
suggest how the
2
4
He was produced.
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 Spring '10
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