Review Reaction mechanism Br 2 (l) step 1 Br 2 2 Br. h step 2Br. + step 3 C 5 H 11. + overall Br 2 C 5 H 12  HBr + C 5 H 11. Br.  C 5 H 11 Br + C 5 H.

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Presentation transcript:

Review Reaction mechanism Br 2 (l) step 1 Br 2 2 Br. h step 2Br. + step 3 C 5 H overall Br 2 C 5 H 12  HBr + C 5 H 11. Br.  C 5 H 11 Br + C 5 H 12 (l)  C 5 H 11 Br (l) + HBr (l)   + C 5 H 12  C 5 H 11 Br+ HBr

Br 2 (l) + C 5 H 12 (l)  C 5 H 11 Br (l) + HBr (l) step 1 Br 2 2 Br. h step 2Br. + step 3C 5 H C 5 H 12  HBr + C 5 H 11. C 5 H 11 BrBr.  assume step 2 is rate determining(slow) rate = k 2 Br. = intermediate [Br. ][C 5 H 12 ] K eq = [Br. ] 2 [Br 2 ] [Br. ] = rate = k 2 k’[Br 2 ] 1/2 [C 5 H 12 ] rate =k’[Br 2 ] 1/2 [C 5 H 12 ] 1 1/2 order reaction K eq 1/2 [Br 2 ] 1/2  

increase [react]  bimolecular elementary steps increase rate of reaction increase T  increase rate of reaction increase number of collisions increase force of collisions

minimum energy required for reaction: activation energy T1T1 T2T2 EaEa # molecules Kinetic Energy T 2 > T 1 = E a

Arrhenius Equation T dependence of a rate constant, k k = ka) increases b) decreases k R = gas constant (8.314 x kJ/K mol) T = temperature (K) z = collision frequency p = steric factor (<1) with T zp e -Ea/RT with E a a) decreases b) increases E a = activation energy (kJ/mol)

p = steric factor z = collision frequency combine to give A k = A e -Ea/RT

Arrhenius Equation k = A e -Ea/RT ln k = y = m x + b ln (k 2 / k 1 ) = plot ln k - (E a /R)(1/T) ln A- (E a /R) (1/T) + ln A v.s. 1/Tslope = -E a /R intercept = ln A (E a /R)(1/T 1 - 1/T 2 ) ln K = - (  H o /R) (1/T) +  S o /R

A-B + C A + B-C A... B... C activated complex P.E. is at a maximum transition state

A-B + CA... B... CA + B-C P.E. Reaction coordinate E af E ab  H rxn reactants products activated complex looks like species closest in energy E ab - E af =  H rxn

P.E. Reaction coordinate E af E ab  H rxn reactants products activated complex exothermicE ab E af > endothermic

products reactants E af E ab P.E. Reaction coordinate activated complex exothermicE ab E af > endothermicE ab E af < large E a = slow rate

- catalyst+ catalyst lowers E af  lowers E ar  K eq unchanged and  H faster forward reaction ( k f ) faster reverse reaction ( k r ) kfkf kr kr = K eq

Br 2 (l) + C 5 H 12 (l)  C 5 H 11 Br (l) + HBr (l)  H rxn Reaction coordinate P.E. Br 2 + C 5 H 12 C 5 H 11 Br + HBr  H rxn < 0 EaEa

P.E. C 5 H 12 + Br 2 C 5 H 11 Br + HBr step 2Br. + C 5 H 12  HBr + C 5 H 11. step 3 C 5 H Br.  C 5 H 11 Br 2Br. + C 5 H 12 HBr + C 5 H Br. EaEa EaEa EaEa Br 2 (l) + C 5 H 12 (l)  C 5 H 11 Br (l) + HBr (l) h step 1 Br 2 2 Br. h  H rxn