__Chapter 19: Nuclear Chemistry
__

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__Section 19-1:Ê Balancing Nuclear Equations__

__Section 19-2:Ê Nuclear Kinetics and Half-Life__

__Chapter 19 Practice Exercises and Review Quizzes__

__Section 19-1: Balancing Nuclear Equations__

During a nuclear reaction, the
nuclei of the isotopes involved will undergo a change in composition. Each particle involved in a nuclear
reaction will be represented as follows, where Z is the atomic number and A is
the mass number:

When a nuclear reaction is
balanced, the sum of the Z values for the reactants must equal the sum of the Z
values for the products. Likewise,
the sum of the A values for the reactants must equal the sum of the A values
for the products. Note that
charges are typically omitted when nuclear reactions are written.

Types of radioactive decay include:

A. Alpha decay (or alpha emission)
= nucleus of an isotope X emits a helium-4 nucleus to produce a new isotope
Y. The equation is balanced as
follows:

B. Beta decay (or beta emission) =
nucleus of an isotope X emits a particle equivalent to an electron to produce a
new isotope Y. The equation is
balanced as follows:

C. Positron decay (or positron
emission) = nucleus of an isotope X emits a particle equivalent to an electron,
but with a positive charge, to produce a new isotope Y. The equation is balanced as follows:

D. Electron capture = electron from
an inner orbital is absorbed into the nucleus of isotope X to produce a new
isotope Y. The equation is
balanced as follows:

In each case above, the identity of
the isotope Y can be determined by matching the atomic number of Y with an
element on the periodic table:

__Sample Exercise 19A:__

Write balanced equations for the
following nuclear reactions:

a. Uranium-235 decays by alpha
emission.

b. Rubidium-87 decays by beta emission.

c. Potassium-38 decays by positron
emission.

d. Iron-55 decays by electron
capture.

__Solution:__

A nuclear reaction may also be
initiated by bombarding a sample of an isotope with particles such as neutrons
or protons in order to produce a new isotope. Other particles may be produced in the process as well. The symbols for a neutron and a proton
are as follows:

__Sample Exercise 19B:__

Neutron bombardment of nitrogen-14
produces a proton and a new isotope.
Write a balanced equation for this nuclear reaction.

__Solution:__

__Section 19-2: Nuclear Kinetics and Half-Life__

The half-life (t_{1/2}) of
a radioactive isotope is the time required for the isotope to decay to half its
initial quantity. Given the
initial quantity (Q* _{i}*)
of the isotope in any unit (such as grams, moles, or number of atoms), the
final quantity (Q

__Sample Exercise 19C:__

The half-life of bromine-80 is 18
minutes. What mass of bromine-80
will remain if a 96 gram sample decays for 72 minutes?

__Solution:__

__Sample Exercise 19D:__

The half-life of potassium-40 is
1.25 x 10^{9} years. How
much time is required for a 4.48 mol sample of
potassium-40 to decay to 0.0700 mol?

__Solution:__

__Sample Exercise 19E:__

A sample of radon-222 containing
6.54 x 10^{25} atoms requires 26.7 days to decay to 5.11 x 10^{23}
atoms. Calculate the half-life of
radon-222.

__Solution:__

__Chapter 19 Practice Exercises and Review Quizzes:
__

19-1) Write balanced equations for
the following nuclear reactions:

a. Lead-196 decays by electron
capture.

b. Phosphorus-28 decays by positron
emission.

c. Radium-226 decays by alpha
emission.

d. Zinc-73 decays by beta
emission.

__Click for Solution__

19-1)

19-2) Proton bombardment of
magnesium-26 produces an alpha particle and a new isotope. Write a balanced equation for this
nuclear reaction.

__Click for Solution__

19-2)

19-3) The
half-life of oxygen-13 is 0.00870 seconds. How many moles of oxygen-13 will remain if a 38.4 mol sample
decays for 0.0696 seconds?

__Click for Solution__

19-3)

19-4) The
half-life of iodine-131 is 8.04 days.
How much time is required for a sample containing 6.56 x 10^{23}
iodine-131 atoms to decay to 8.20 x 10^{22} atoms?

__Click for Solution__

19-4)

19-5) A 48
gram sample of magnesium-28 requires 84 hours to decay to 3.0 grams. Calculate the half-life of
magnesium-28.

__Click for Solution__

19-5)