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NUCLEAR CHEMISTRY. COMPARE THE FOLLOWING REACTIONS. PbCl 2 + Li 2 SO 4 PbSO 4 + 2LiCl 2Al + Fe 2 O 3 2Fe + Al 2 O 3 14 7 N + 4 2 He 17 8 O + 1 1 H. Nuclear Chemistry : The branch of chemistry that deals with nuclear reactions, changes in the atomic nucleus Isotopes
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COMPARE THE FOLLOWING REACTIONS • PbCl2 + Li2SO4 PbSO4 + 2LiCl • 2Al + Fe2O3 2Fe + Al2O3 • 147N + 42He 178O + 11H
Nuclear Chemistry: • The branch of chemistry that deals with nuclear reactions, changes in the atomic nucleus • Isotopes • Are atoms having the same atomic number (# of protons) but different mass numbers (# of neutrons) • Radioisotope • An atom having an unstable nucleus • Radioactivity • The spontaneous disintegration of an unstable atomic nucleus with the accompanying emission of radiation
Rules for Writing Equations for Nuclear Changes • Mass number is conserved in a nuclear change • Electric charge is conserved in a nuclear change
Nuclear Equations • Transmutation • change one element into another • Types of Nuclear Reactions • Alpha emission (42He) • 21184Po 42He + 20782Pb • 21986Rn • Beta emission (0-1e) • 21083Bi 0-1e + 21084Po • 22387 Fr
Positron decay (0+1e) • 116C 0+1e + 115B • K-capture (0-1e) • 10046Pd + 0-1e 10045Rh • 8337Rb
RULES OF LOGARITHMS • log xy = log x + log y • log x/y = log x – log y • log xy = y log X
Half life • The length of time necessary for one half an amount of a radioactive nuclide to disintegrate original mass (1/2)x = final mass where x = number of half lives
The half life of Ba-131 is 12 days. How much of a 50.0 g sample will remain after 36 days? • 3 half lives (1/2)3 • 50.0 g (1/2)3 = x • x = 6.25 g • If you start with 2.97 x 1022 atoms of Mo-91, how many atoms will remain after 62.0 minutes? The half life of Mo-91 is 15.49 minutes. • 4 half lives (1/2)4 • 2.97 x 1022 (1/2)4 = x • x = 1.86 x 1021atoms
What is the half-life of a radioactive isotope if a 100.0g sample decays to 12.5 g in 24.0 hours? original mass (1/2)x = final mass 100.0 g (1/2)x = 12.5 g (1/2)x = 0.125 log (1/2)x = log 0.125 x log (1/2) = log 0.125 x = 3 half lives 24.0 hrs/3 = 8 hrs
How old is a bone if it presently contains 0.0625g of C-14, but it was estimated to have originally contained 1.000g of C-14 (half life = 5730 yr)? original mass (1/2)x = final mass 1.000g (1/2)x = 0.0625 g (1/2)x = 0.0625 log (1/2)x = log 0.0625 x log (1/2) = log 0.0625 x = 4 half lives 4 ( 5730 years) = 23,000 years