Ch ical chemistr Reaction Kinetic Rice-Herzfeld mechanisms a chain reaction can lead to a simple rate law yrolysis of acetaldehyde CH3CHO(8)-4 >CH4(8)+CO(g) dt-kICH3CHOJ/2 d[Ch4 Simple rate laws can follow from quite complex chain mechanisms The Rice -Herzfeld mechanism for the pyrolysis of acetaldehyde is (a)Initiation: CH3CHO ka、CH3+CHO r=kalch3chol (b) Propagation ChaCHO +oCHa kB CHA+CHaCO. r=kb[CH3 CHOJ. 1 (c) Retardation:CH3CO、k。CH3+CO r=kclCH3. Termination: CH3 +oCH kd CH3CH,3 Physical Chemistry Rice-Herzfeld Mechanisms Simple rate laws can follow from quite complex chain mechanisms. (a) Initiation: CH CHO a CH CHO k ⎯⎯→• +• 3 3 [ ] r = ka CH3 CHO (b) Propagation: CH CHO +•CH ⎯⎯→CH +CH CO• b k 3 3 4 3 [ ][ ] CH3 CHO CH3 r kb = • (c) Retardation: CH CO c CH CO k 3 • ⎯⎯→• 3 + [ ] 3 r = k CH CO• c (d) Termination: CH3 CH3 CH3 CH3 d k • +• ⎯⎯→ 2 3 r k [ CH ] d = • The Rice-Herzfeld mechanism for the pyrolysis of acetaldehyde is A chain reaction can lead to a simple rate law. Pyrolysis of acetaldehyde ( ) ( ) ( ) CH3 CHO g ⎯⎯→CH4 g +CO g  3/ 2 3 4 [ ] [ ] k CH CHO dt d CH = Reaction Kinetics