1. Reaction Mechanisms

2. Reaction Mechanisms
Most reactions occur in a series of elementary steps
These steps together are called the reaction mechanism
Molecules that form in one step and are consumed in the next are called reaction intermediates

3. 2N2O(g)  2N2(g) + O2(g) Step 1: Step 2: (slow) (fast)
Reaction Mechanism
Step 1:
Step 2:
(slow)
(fast)
2N2O(g)  2N2(g) + O2(g)
Intermediate

4. Rate-Determining Step
Each elementary step has its own rate
The overall rate of a reaction is determined by the rate of the slowest step, the rate-determining step (RDS)
Therefore, the rate law for the rate-determining will be the rate law for the overall reaction
The molar coefficients in the RDS will be the exponents in the overall rate law

6. Overall rate law depends on the RDS.
Reaction Mechanism
Step 1:
Step 2:
(slow)
(fast)
2N2O(g)  2N2(g) + O2(g)
Intermediate
Overall rate law depends on the RDS.
Molar coefficients of RDS will be the exponents.
r = k[N2O]

7. Practice
P. 390 #2
P. 391 #1,2,3abcd
Worksheets