5CHM11509 HIK and students (1)

# 5CHM11509 HIK and students (1) - CHM 115 Dr Hilkka Kenttmaa...

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CHM 115 Dr. Hilkka Kenttämaa Lecture 5 Reading was: 23.4 and 23.5 Lecture 6: 23.7-23.9

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Summary from Previous Lecture E = mc 2 mass defect Nuclear reactions are different from other chemical reactions Atoms change identity Energy scale different Types of nuclear reactions vary and can be predicted
Radioactive Decay Follows First-order Kinetics 6 h 6 h 6 h 6 h t 1/2 = 6 h half-life

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Buddy Question # 1 X is radioactive. How much of a sample of X is left after 3 half-lives a. 1/2 b. 1/3 c. 1/4 d. 1/8 e. Impossible to tell without knowing the initial mass of X and its half life
Buddy Question # 1 X is radioactive. How much of a sample of X is left after 3 half-lives a. 1/2 b. 1/3 c. 1/4 d. 1/8 e. Impossible to tell without knowing the initial mass of X and its half life One half-life Two half-lives

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The half-life of 239 Pu is 24,000 years. How much 239 Pu remains in a sample that initially contained 1.0 kg of plutonium after 96,000 years? a. 1/2 kg b. 1/4 kg c. 1/8 kg d. 1/16 kg Buddy Question # 2
The half-life of 239 Pu is 24,000 years. How much 239 Pu remains in a sample that initially contained 1.0 kg of plutonium after 96,000 years? a. 1/2 kg b. 1/4 kg c. 1/8 kg d. 1/16 kg Buddy Question # 2 Time / half-life = # half-lives 96,000 y / 24,000 y = 4 => 4 half-lives 1 kg => 0.5 kg => 0.25 kg => 0.125 kg => 0.0625 kg = 1/16 kg 1 2 3 4

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Nuclear Reactions’ Kinetics N = # decaying nuclei dN / dt = change in # of nuclei per s (or min, hr, . ..) First order rate equation: dN / dt = - k N Integrated rate equation: ln (N/N o ) = - k t N 0 = initial #; N = # at time t k = rate constant with a value depending on the nucleus Reaction rate is independent of the concentration of N
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## This note was uploaded on 02/06/2012 for the course CHM 115 taught by Professor Towns during the Spring '08 term at Purdue.

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5CHM11509 HIK and students (1) - CHM 115 Dr Hilkka Kenttmaa...

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