Nuclear Chemistry Particles Energy Nuclear reactions

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Nuclear Chemistry Particles
Energy Nuclear reactions mass
defect Nuclear Stability Mentor
Sessions ?????
Fred J. Grieman
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Last Semester Mostly Macroscopic Chemistry This
Semester Microscopic Basis of
Macroscopic Start with study of nucleus Why?
1) Important for society creation operation
of universe
nuclear energy
radiochemistry and biology
2) lab experiment neutron activation
excellent analytical technique for
metals 3) concepts of energy and mass E
mc2 (However, rest of course only
mass charge
of nucleus important)
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http//www.astro.uva.nl/demo/sun/corona.htm
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Nuclear Reactions in Sun as example
1H 1H ? 2H Deuteron 2H
1H ? 3He2 3He2 3He2 ? 4He2 2
1H

41H ? 4He2
hydrogen burning Change in mass releases
enormous energy Large decrease in number of
particles Older stars nucleosynthesis how
elements are made 4He2 ? 8Be4
? 12C6 ? Young star ? red giant ? white
dwarf ? super
nova (gives heavier elements) V.E. Viola, J.
Chem. Ed., Vol. 67 (1990) 723
x 2
Expansion vs. Contraction
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• The Basics Particles
• Nucleus protons neutrons
• 1) proton 11p
• 2) neutron 10n
• Beta (ß) particle in nuclear reactions
• 3) electron -01e- (Sometimes
  written as -01ß- )
• Symbols
• Z atomic (total protons)
• N neutron (total of neutrons)
• A mass ZN
• hydrogen atom 11H hydrogen nucleus 11H

mass
charge
atomic
Table 15-1 for mass
Symbol AZEl
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Nuclides different nuclei w/ different Z A
Used when specifying nuclear composition 11H,
21H, 42He Isotopes different nuclides w/ same
Z 11H vs. 21H 42He vs.
32He Remember Average atomic mass from sum
of mass of isotopes
times fractional abundance Other particles
Alpha particle, a, 42He2 Beta particle, ß,
-01e- Neutrino, ? (very small mass,
chargeless, ang. mom. conservation,
reacts very weakly
with matter) Antimatter same mass, but
opposite charge
Transient existence matter/antimatter ?
annihilation reactions Antiproton -11p-
Positron (antielectron) 01e (we will use)
Antineutrino ? (we will use but not
explain thoroughly) Annhilation reaction
-01e- 01e ? 2 00? (gamma rays!!!)

(mass changing to energy!!!)
Table 15-1

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The Basics Energy 1) Electromagnetic energy
(light) oscillating E B fields (more later)
?-ray nuclear processes changes in
nuclear energy states (physics) X-ray
core (inner) electrons removed,
valence (outer) e- ? core releases
X-ray Ultraviolet, visible valence e-
move in valence shell Infrared
vibrations in molecules Microwave
rotation of molecules 2) Particle energy
(Total) E (Kinetic) EK (Potential)
EP EK energy of motion EP energy
of position Graph
E
Energy
EK

EP
position
(p. 101 for vocab.)
E
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The Basics mass, energy, and units Nuclear
reactions mass ? energy (electromagnetic
and/or EK) 1) Mass defect is ?m in nuclear
reactions Atomic mass unit (amu) u more
convenient than kg or g 1 g 6.0221420 x
1023 u No u Molar mass M(Atom) (g) ?
m(Atom) (u) 2) mass ? energy via E mco2
(special theory of relativity) ?E ?m co2
co speed of light in a vacuum Calculate ?E
for ?m 1 u ?E 1u (1g/6.022142x1023u)
(1kg/1000g) (2.99792 x 108 meter/sec)2
1.492418 x 10-10 J/u Is this a lot or a
little?
Table 15-1
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?E 1.492418 x 10-10 J/u For 1 mole ?E
(J/mole) ?E(J/u) No 8.9875 x 1010 kJ/mole
Is this a lot or a little? Chemical bond
energy? Combustion of methane
CH4 2O2 ? CO2 2H2O ?Erxn -56
kJ/mol So large use different unit MeV
(megaelectron volt) 106 eV 1 MeV
1.602176 x 10-13 J ?m 1 u ?E 931.494
MeV (Tables often given in these units) Basics
now down ? nucleus and nuclear stability
4 x 102 kJ/mole
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Nuclear Stability 1) Nuclear Equations
Like Chemical Reactions except a) Z and A
must balance b) ?m ? 0 !!! Examples
of balancing equations i) Sun, from before
4 11H ? 42He2 not balanced
Z4, A4
Z2, A4 (Z4 ? Z2) What particle do we
need to balance? A 0 Z 2?

? 01e (x2)
Balance 4 11H ? 42He2
2 01e Actual process lots of e-s
in Sun ( -01e- 01e ? 2 00? ) x2
annihilation rxn


from before
4 11H 2 -01e-
? 42He2 energy ii) Upper atmosphere
147N
? ? 146C 11H
Z7, A14 Z7, A15

? 10n
147N
10n ? 146C 11H

balanced
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2) Binding energy of nuclei from ?m 8 11H
8 10n ? 168O ?Erxn ?m co2
?m m(168O) - 8m(11H) - 8m(10n)
15.9949 - 8(1.0078) - 8(1.0087)
From 15-1 (with more sig. fig.s) -
0.13700 u lt 0 !! so 168O is more stable
- 0.13700 u (931.494 MeV / u)
- 127.62 MeV ?Erxn lost mass to energy ? EK
of product Binding Energy Eb(168O) -
?Erxn 127.62 MeV For comparison Binding
Energy/nucleon Eb/A
127.62/16 7.976 MeV/nucleon
Stability from Thermo?
If ?G lt 0, 168O stable
?G ?H - T?S const P, T
?E ?PV - T?S
?E gtgt ?PV, ?S so only consider ?E
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• 3) Nuclear Stability
• 168O 168O ? 3216S Which
  is more stable?
• ?m -0.017759 (Table 15-1) ? ?E
  -16.5424 MeV
• ?
  Eb (3216S) 271.78 MeV
• ?
  Eb/A (3216S) 8.4932 MeV/nucleon
• 
  Eb/A (168O) 7.967 MeV/nucleon
• 3216S is more stable!!! Does this
  surprise you?
• ?? O2 molecules should become S atoms ???
• Explore this next time

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