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Unformatted text preview: Lecture 36 1 Reaction Dynamics: Cross-Sections (Chapter 30.1-4) We are now ready to combine our knowledge of gas-phase kinetics with kinetic gas theory. As I said earlier, two molecules cant react unless they collide. Therefore the bimolecular rate constant, must be related to the binary collision rate, Z AB . For an elementary bimolecular reaction: [ ] [ ][ ] Products, v k d A A B k A B dt + = - = First lets assume that the reaction can occur if we have a hard-sphere collision. We have already learned that -1 3-1 AB 3-1-1 3 3 1/2 2 AB Since k has units of sec dm mol and has units of m molec sec , this is easy to fix: 1000 8 where and and 2 r A AB r A B B A B r A u dm molec k N u m mol d d k T m m u m m = + = = = + B v AB AB r A B Z u = = Lecture 36 2 How well does this work for a very reactive binary collision? ( 29 ( 29 5 3-1-1 3 2 2 7.59 10 dm mol sec k O g O g O k + = 3 3 o o O 3 O 2 2 o 19 2 1/2 For O, 1.80A; For O , 5.16A 38A 3.8 10 2 8 at 298K 725 / O O B r d d d d m k T u m s - = = + = = = = = 11 3-1 -1 1.66 10 dm mol s1....
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