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L41-Nuclear3

# L41-Nuclear3 - Energy of nuclear transformations mass...

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Energy of nuclear transformations - mass defect and Einstein mass-energy relation - star chemistry (fusion) - nuclear power (fission) Mike Hour , Grant Powers, 1946 (Combat Art Division, United States Marine Corps Water color on paper)

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Mass defect and energy-mass inter-conversion in nuclear transformations Nuclear transformations: mass number A and charge number Z are conserved 238 92 U -> 4 2 He + 234 90 Th A: 238 = 4 + 234 Z: 92 = 2 + 90 MASS is not conserved in nuclear rxns! It is converted to ENERGY E=mc 2 or D E= D mc 2 , where c=2.9979x10 8 m/s
How to calculate energy of nuclear reactions? Consider fusion rxn (1919, Rutherford): 14 7 N + 4 2 He -> 17 8 O + 1 1 H + D E D E= S ( D E f ) products - S ( D E f ) reactants D E f : energies of formation of a nucleus from nucleons, e.g.: 8 1 0 n + 8 1 1 H -> 16 8 O + D E f by using E=mc 2 formula: D E f =[m( 16 8 O) 8*m( 1 1 H)-8*m( 1 0 n)]c 2 = -2.269x10 -28 kg* c 2 =-6.8x10 -12 J

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Formation of nuclides from neutrons and protons: “exothermic” Binding energy per nucleon: E b = D E f /n
The following fusion rxn describes how energy is produced in Sun and many other stars: 1 H + 1 H -> 2 H + 0 +1 e 2 H + 1 H -> 3 He + 0 0 g 3 He + 1 H -> 4 He + 0 +1 e Overall: 4 1 H -> 4 He + 2 0 +1 e Calculate energy released by formation of one mole of 4 He by the above rxn. Compare this energy with the energy released by burning the same amount of hydrogen

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L41-Nuclear3 - Energy of nuclear transformations mass...

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