Lecture+2+-+Chemical+Kinetics

Lecture+2+-+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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Kinetic Theory of Gases Summary 3. Molecular Binary Collision Frequency (Z 11 or Z AB ) : 4. Rate of Gas Phase Reaction: () 1 3 35 3 25 9 1 11 10 10 5 . 2 2 / 10 2 = × = = s m collisions m s collisions V N Z Z 1 8 11 10 s M Z Rate = (# of collisions per second, Z 11 ) X (exp(- E a /RT) Fastest rate = Z 11 X exp(-0/RT) = 10 8 M s -1 2. Average molecular speed (c) determined by Maxwell Distribution: M RT c rms 3 = M RT c mp 2 = R = 8.314 J mol -1 K -1 T = Temp (K) M = molar mass (kg/mol) 1 J = 1 kg m 2 s -2 = V N d c Z 2 1 2 π Mean free path ( λ ) = <c>/Z 1 = 640 Ǻ M RT c 8 = 475 m/s 515 m/s 421 m/s 1. Molecular velocity and energy vs Pressure, Volume and Temp: 3 2 v Nm PV = 3 2 trans E N PV = T k E B trans 2 3 =
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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. P R Reactant Product [R](t) [P](t) Time Concentration [] [ ] Δ t P Δ = Δ Δ = t R rate 0 ] [ < Δ Δ t R Minus sign because (i.e. [R] decrease vs t)
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Instantaneous Rate of Reaction [] [ ] dt R d dt P d = = rate Reaction rate at specific time point (t 1 ) is called instantaneous rate. [R](t) [P](t) Time Concentration t 1 P R Instantaneous rate equals the slope of the tangent at a specific time (t 1 ). 0
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This note was uploaded on 08/07/2011 for the course CHE 107B taught by Professor Ames during the Summer '11 term at UC Davis.

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Lecture+2+-+Chemical+Kinetics - Rate Depends on Collision...

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