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7/29/2019 m13 Nuclear Energy
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Nuclear Energy
7/29/2019 m13 Nuclear Energy
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Mass and energy Einstein suggested that mass and energy
are related by E=mc2
(c = 3.0 x 108
m/s)
E: energy, m: mass, c: speed of light
Converting the mass of one penny could
provide the entire energy requirementsfor 700 people for one year
Power a space heater for 7000 years
Thats about $3 million worth of electricity
Because mass and energy are related thelaw of conservation of energy and law of
conservation of mass can be combined into
the Law of Conservation of Mass - Energy
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Fission and Fusion Chemical reactions involve outer electrons
Nuclear reactions involve changes in nuclei Two types of nuclear reactions are fusion and
fission(othersareradiationandtransmutation)
Fission is when a nucleus breaks apart Fusion involves adding nucleons to a nucleus
Fission is used in nuclear power plants andpowered the first atomic bomb (21 kilotons)
Fusion powers stars and may also be used inthermonuclear bombs (60 megatons)
Fusion requires that the nucleons be close
enough so that the strong force can form
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Nuclear forcesThere are two opposing forces in the nucleus:
Electrostatic (+ve proton repels +ve proton)Strong force (nucleons attract each other)
The strong force is stronger, but acts over a
shorter distance. Adding more nucleons isfavored with small nuclei but not with large
E.g. adding a proton to a small vs. large nucleus
(see figure 23.1 on pg. 960)
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Radioactivity Radiation is the release of particles or energy
Several types have been observed:1) 42He, 2)
01e, 3)
01e, 4)
00, 5)
X-rays
1. 42He are called alpha () particles
I.e. mass of 4 amu, charge of +2 (2 p+, 0 e
)2. 01e is an electron:beta() particle if released,
electron capture if taken from first orbital
3. 01
e is given the name positron (aka +)
4. 00 is called gamma radiation. It is released
when the nucleus has too much energy.
5. X-rays are given off when there is an electron
capture (EC) (as electrons jump down shells)
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Converting protons and neutrons There are certain combinations of protons and
neutrons that are more stable than others If the number of protons:neutrons is not
correct the nucleus is unstable.
The solution is to release certain types ofradioactivity. Note: proton (11p), neutron (
10n)
10n 11p + 01e ( emission)
11p 10n + 01e (+ emission)
11p +
01e 10n (EC electron capture)
You can tell what type of reaction will occur byreferring to the top of your periodic table
(Table of Selected Radioactive Isotopes)
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Nuclear equationsQ. Write the nuclear
equation for C-14
In all cases follow these steps:1) determine the type of decay2) balance charge and mass of particles
Practice: pg. 1001, 23.23, 23.27
For more practice try .24, .25, .26 and .28.
C
14
6
e
0
-1 N
14
7+
Po209
84 He42 Pb
20582+
Q. Write the nuclear
equation for209Po
Q. Complete this fission reaction
Kr9436
U235
92 n10 Ba
13956+n
10+ 3 +
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Rate limiting steps Many chemical, nuclear and biological
reactions undergo several steps A rate limiting step is a slow step that
causes a backlog in the reaction
A focus on these steps is important inchemistry because the slowest step
determines the rate of the overall reaction
In biology these steps are often the focus of
modification by enzymes since changingthese will have the greatest affect.
Q what is the rate limiting step in converting
U-238 to U-234 (fig. 23.4, pg. 965)
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Nuclear energy Read pg. 959 (starting at 23.2) to 961.
1. Define: binding energy, nucleon, fission,nuclear fusion, radioactivity, half-life.2. What evidence exists that mass and energy
are interchangeable?
3. Which elements are most stable? Whichcan undergo fusion reactions? Which canundergo fission reactions?
4. What are the opposing forces that existwithin the nucleus?5. Explain how these two forces account for
the region of stability in fig. 23.1.
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1. Binding energy: the energy that holds
nucleons together
Nucleon: protons and neutrons
Nuclear fission: breaking apart nucleiNuclear fusion: forming or adding to nuclei
Radioactivity: releasing small particles or
energy from a nucleusHalf-life:time taken to lose the radioactivity
2. The existence of binding energy is evidence
that mass can be converted to energy3. Fig. 23.1: elements (e.g. Fe-56) in the region
of stability are most stable. Elements to the
left (e.g. H-2) can undergo fusion, elements to
the right (e.g. 120Sn) can undergo fission.
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4. The strong force attracts adjacentnucleons. Electrostatic repulsion of protons
pushes protons away from each other.5. H has only a few nucleons, Fe has more.
Thus, iron has more attractive forces holding
the nucleus together. Smaller elements thanFe will fuse to get more net strong force.Large nuclei have more protons (more
electrostatic repulsions) and can more easily
separate. The strong force cannotcompensate because it acts over very short
distances. Its a balance between attraction
and repulsion. For more lessons, visitwww.chalkbored.com
http://www.chalkbored.com/http://www.chalkbored.com/