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MIT OpenCourseWare http://ocw.mit.edu 5.111 Principles of Chemical Science Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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32.1 5.111 Lecture 32 Kinetics Topics: Radioactive Decay, Second Order Integrated Rate Laws, Kinetics and Chemical Equilibrium, Introduction to Reaction Mechanisms Chapter 13 (p 498-501, 507-508) and Chapter 17 (p 660-664) Radioactive Decay The decay of a nucleus is ____________ of the number of surrounding nuclei that have decayed. We can apply first order integrated rate laws: [A] = [A] 0 e -k t and t 1/2 = 0.6931 k However, instead of concentration, the first order integrated rate law is expressed in terms of N (number of nuclei) N = N o e -k t k decay constant t time N 0 number of nuclei originally present Chemical kinetics – monitor changes in concentration over time Nuclear kinetics – monitor rate of occurrence of decay events with a Geiger counter (radiation detector) Decay rate is also called Activity (A) Activity = A = -dN = k N dt because activity is proportional to the number of nuclei (N): N = N o e -k t can be expressed as A = A o e -k t A Activity A 0 original activity S.I. unit for Activity is the becquerel (Bq) 1 Bq 1 radioactive disintegration per second
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