Lecture 3 - Chemical Kinetics

Lecture 3 - Chemical Kinetics - Rate Depends on Collision...

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A + B Product E a Rate = (# of collisions per second) X (fraction collisions having E > E a ) exp(-E a /RT) Rate Depends on Collision Frequency (Z 11 ) and Boltzmann Factor (e -Ea/RT ) P Rate = { Z 11 (10 8 M s -1 ) } X { exp(-0/RT) } = 10 8 M/s 2 2 11 2 2 = V N c d Z π If every collision produces product, then Rate = 10 8 M/s (upper limit). Fastest reaction rate in solution is ~10 10 M/s for H + + OH - H 2 O
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1 9 1 3 25 2 2 10 1 10 6 ) 10 46 . 2 )( / 10 5 ( ) 10 4 ( × × × × = s Z m s m m Z π Collision Frequency (Z 1 ) For one molecule: Volume of cylinder: Z 1 = Volume of cylinder X density of molecules time Number density: collisions s -1 ~10 9 Collisions by a single molecule in one second. area x length at 298 K V N t t c d Z 2 1 ( ) ( ) t c d 2 L V N 1 10 46 . 2 22 × =
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Mean Free Path ( λ ) λ is average distance traveled between collisions. λ = average speed (c) X average time between collisions (1/Z 1 ) 640 / 10 4 . 6 / 10 5 . 7 10 8 . 4 6 9 1 4 1 = × = × × = = collision cm s collisions s cm Z c Ǻ P d T k V N d V N c d c Z c B 2 2 2 1 2 2 1 2 π = = = = T k P RT PN V N B A = =
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Sucrose + Air Metabolic Energy Chemical Kinetics (Chapter 9) O 11H 12CO 12O O H C 2 2 2 11 22 12 + + Δ = -5693 kJ/mol Ch. 9 Homework : 2, 4, 6, 8, 10, 12, 14, 16, 20, 22, 23, 26, 27, 32, 34, 38, 50, 51, 53, 56, 57, 60, 64 Δ Sucrose CO 2 + H 2 O E a Rate (k) exp(-E a /RT) K eq exp(- Δ Gº/RT) Enzyme Catalyzed (fast) No enzyme (slow) K eq ~ 10 100
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Reactant and Product vs Time Why Study Chemical Kinetics? Learn how to control and optimize reactions Predict the yield and outcome of a reaction Deduce the molecular mechanism a reaction (i.e. how many steps) What is Chemical Kinetics? Kinetics investigates the rate of chemical reactions and how rate depends on temperature, concentration and catalysts.
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This note was uploaded on 04/06/2011 for the course CHEM 107B taught by Professor Jamesames during the Winter '09 term at UC Davis.

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Lecture 3 - Chemical Kinetics - Rate Depends on Collision...

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