Lecture_4_3_09 - Chapter 20: Nuclear Chemistry Mass-Energy...

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Chapter 20: Nuclear Chemistry
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2 Mass-Energy Calculations When nuclei decay, they form products of lower energy. The change of energy is related to the change in mass , according to the mass-energy equivalence relation derived by Albert Einstein in 1905. Energy and mass are equivalent and related by the equation 2 mc E = Here c is the speed of light, 3.00 x 10 8 m/s.
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3 Mass-Energy Calculations When nuclei decay, they form products of lower energy. If a system loses energy , it must also lose mass . Though mass loss in chemical reactions is small (10 -12 kg), the mass changes in nuclear reactions are approximately a million times larger.
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4 Mass-Energy Calculations When nuclei decay, they form products of lower energy. Consider the alpha decay of uranium-238 to thorium- 234. He Th U 4 2 234 90 238 92 + We have written the atomic mass (in amu) beneath each nuclide symbol. 238.05078 234.04359 4.00260
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5 Mass-Energy Calculations When nuclei decay, they form products of lower energy. The change in mass for this reaction, in molar amounts is He Th U 4 2 234 90 238 92 + 238.05078 234.04359 4.00260 g 00459 . 0 ) 05078 . 238 00260 . 4 04359 . 234 ( m - = - + =
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6 Mass-Energy Calculations When nuclei decay, they form products of lower energy. The change in mass for this reaction, in molar amounts is He Th U 4 2 234 90 238 92 + 238.05078 234.04359 4.00260 g 00459 . 0 m - = The energy change for 1 mol of uranium-238 is 2 8 6 2 m/s) 10 (3.00 kg) 10 59 . 4 ( mc E × × × - = = - kJ 10 -4.13 J 10 13 . 4 E 8 11 × = × - =
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This note was uploaded on 02/26/2012 for the course CHEM 108 taught by Professor Dr.brennan during the Spring '09 term at Binghamton University.

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Lecture_4_3_09 - Chapter 20: Nuclear Chemistry Mass-Energy...

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