33_562ln08

33_562ln08 - MIT OpenCourseWare http:/ocw.mit.edu 5.62...

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MIT OpenCourseWare http://ocw.mit.edu 5.62 Physical Chemistry II Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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5.62 Spring 2007 Lecture #33 Page 1 Transition State Theory. I. Transition State Theory = Activated Complex Theory = Absolute Rate Theory H 2 + F ! " [H 2 F] k ! " ! HF + H Assume equilibrium between reactants H 2 + F and the transition state. Treat the transition state as a molecule with structure that decays unimolecularly with rate K = [H 2 F] [H 2 ][F] constant k. d[HF] dt = k H 2 F [ ] = kK H 2 [ ] F [ ] k has units of sec –1 (unimolecular decay). The motion along the reaction coordinate looks like an antisymmetric vibration of H 2 F , one-half cycle of this vibration. Therefore k can be approximated by the frequency of the antisymmetric vibration ν [sec –1 ] k ν ≡ frequency of antisymmetric vibration (bond formation and cleavage looks like antisymmetric vibration) d[HF] dt = ν K [H 2 ] [F] d[HF] dt = ν (q ‡* /N) q *H 2 N ( ) (q F /N) ! " # # $ % e E /kT H 2 [ ] F [ ] K = (q trans /N) q trans H 2 N ( ) ! " # # $ % q rot q rot H 2 ( ) * + , q vib ‡* q vib *H 2 ( ) ) * + , , g 0 g 0 H 2 g 0 F ( ) * + , e - E kT Reaction coordinate is antisymmetric vibrational mode of H 2 F . This vibration is fully excited (high T limit) because it leads to the cleavage of the H–H bond and the formation of
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This note was uploaded on 11/27/2011 for the course CHEM 5.43 taught by Professor Timothyf.jamison during the Spring '07 term at MIT.

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33_562ln08 - MIT OpenCourseWare http:/ocw.mit.edu 5.62...

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