Unit 8 Section 2:
Nuclear Reactions
An Introduction to Nuclear Fission
and Fusion
Objectives:
• Explain that nuclear reactions deal with
interactions between the nuclei of atoms and
chemical reactions occur when electrons
interact.
• Describe the relationship between matter and
energy.
• Explain and differentiate between nuclear
fission and nuclear fusion.
• Understand that both fission and fusion
processes deal with matter and energy.
Nuclear Energy vs. Chemical Energy
• What is the difference between nuclear
and chemical energy?
• Chemical Energy: Energy that is released
during chemical reactions. Chemical
energy involves electrons.
• Nuclear Energy: Energy that is released
from the atomic nucleus. This involves
much larger energies than chemical
reactions.
Matter and Energy
• Recall the law of
conservation of
energy:
• Energy cannot be
created or destroyed.
• New concept:
• Matter and energy
are 2 forms of the
same thing
Einstein’s Famous Equation:E = mc2
• Matter can be changed into Energy
• Einstein’s formula tell us how the change
occurs
• In E = mc2,
• E = Energy
• m = Mass
• c = Speed of Light (Universal Constant)
E=
2
mc
• The equation can be read as follows:
• Energy (E) is equal to Mass (m) multiplied
by the Speed of Light (c) squared
• This tells us that a small amount of
mass can be converted into a very large
amount of energy because the speed of
light (c) is an extremely large number
• c = 3.0 x 108 m/s
Fission: What is it?
• Fission:
• The process of
splitting an atomic
nucleus into fission
fragments.
• Fission
fragments(products):
• In the form of smaller
atomic nuclei and
neutrons
• Releases radiation
Fission (cont’d)
• LARGE amounts of energy are produced by
the fission process
• Fission involves heavy atoms with a lot of
protons and neutrons (nucleons)
• How and why does fission happen?
• How: the nuclei of the heavy atoms are hit by
neutrons; this starts the fission process.
• Why: fission occurs because of the electrostatic
repulsion created by large numbers of protons
within the nuclei of heavy atoms.
Example of Fission Reaction
• Start with:
• U-235 + 1 neutron
• Product:
• 2 neutrons + Kr-92
+ Ba-142 + Energy
Explanation of Fission Reaction
• Explanation:
• A neutron hits an atom of U-235.
• It absorbs the neutron and becomes U-236
which is unstable.
• Fission occurs and more neutrons are
released in the reaction.
• The stray neutrons strike other U-235
atoms to start a nuclear chain reaction.
The Fission Process
Fission (cont’d)
• The fission process is
NATURAL
• There was a natural
uranium reactor in West
Africa over 2 billion years
ago.
• Why is fission useful?
• It generates a large
amount of energy and
this heat can be captured
by nuclear power plants
to produce electricity.
What elements are good for fission?
• Uranium 235 (U-235)
• Uranium 238 (U-238)
• Elements with an
atomic number higher
than 92 do not exist in
nature; they are also
good for the fission
process.
Fusion: What is it?
• Fusion:
• A nuclear reaction in which two light nuclei
combine or fuse to make a larger, heavier
nucleus.
• This process generates LOTS of energy
(Remember E = mc2).
• In order for fusion to begin, a large amount of
energy is needed to overcome the electrical
charges of the nuclei and fuse them together.
Fusion Facts
• Fusion reactions DO
NOT occur naturally on
our planet, but nuclear
fusion is what powers
the stars.
• The sun fuses
hydrogen atoms to
produce helium,
subatomic particles,
and a large amount
of energy.
Diagram of Nuclear Fusion
Review
• Mass and energy are two forms of the same
thing; neither can be created or destroyed,
but mass can be converted into energy (E =
mc2).
• Fission is a nuclear reaction in which:
• A heavy atomic nucleus is split into lighter atomic
nuclei.
• Fusion is a nuclear reaction in which:
• 2 light nuclei are combined into a single, heavier
atomic nucleus.
Quiz Question #1
• Which nuclear process produces large
amounts of energy?
A. Fission
B. Fusion
C. Both fission and fusion
D. Neither fission or fusion
Quiz Question #1
• Which nuclear process produces large
amounts of energy?
A. Fission
B. Fusion
C. Both fission and fusion
D. Neither fission or fusion
Quiz Question #2
• Fission is the process that __________
atomic nuclei.
A. combines
B. burns up
C. stores
D. splits
Quiz Question #2
• Fission is the process that __________
atomic nuclei.
A. combines
B. burns up
C. stores
D. splits
Quiz Question #3
• Mass may be converted into energy.
A. True
B. False
Quiz Question #3
• Mass may be converted into energy.
A. True
B. False
Quiz Question #4
• The fission process requires heavy
atomic nuclei.
A. True
B. False
Quiz Question #4
• The fission process requires heavy
atomic nuclei.
A. True
B. False
Quiz Question #5
• Name the nuclear
reaction that occurs
within the sun.
Quiz Question #5
• Name the nuclear
reaction that occurs
within the sun.
• Nuclear Fusion
Quiz Question #6
• Fission is a natural process that occurs
on the planet earth.
A. True
B. False
Quiz Question #6
• Fission is a natural process that occurs
on the planet earth.
A. True
B. False
Quiz Question #7
• Explain this equation:
• E = mc2
Quiz Question #7
• Explain this equation:
• E = mc2
• Energy is equal to mass times the speed of
light squared.
https://www.youtube.com/watch?
v=KWAsz59F8gA