1. Reaction Mechanisms
Chemical Kinetics-5

2. Reaction Mechanisms
Series of elementary steps reactions go through to completion
Sum of steps must = overall reaction
Mechanism must agree with experimental rate law
Molecularity:
Unimolecular step: one molecule/atom as reactant
Bimolecular step: 2 molecules/species as reactants
Termolecular step: very, very, very rare.
Rate determining step matches the rate law because reaction cannot proceed faster than its slowest step.
Rate law can be written from rate determining step
Intermediates cannot be in the rate law.

3. Example A) Rate determining step, RDS? B) Rate law?
C) Overall reaction?
D) Intermediates?
H2O2  2 OH slow
H2O2 + OH-  H2O + HO fast
HO2 + OH-  H2O + O fast
Catalyst: Accelerates reaction by providing an alternate mechanism with lower activation energy.

4. A + B  C fast A + C  D slow A) Rate determining step, RDS?
B) Rate law?
C) Overall reaction?
D) Intermediates?
A + B  C fast
A + C  D slow