Practice: Consider the following elementary steps:
NO2 (g) + NO2 (g) → NO4 (g) + NO (g) [SLOW]
NO (g) + CO3 (g) → N (g) + CO4 (g) [FAST]
What is the rate law of the reaction mechanism?
A Reaction Mechanism is a step-by-step sequence of elementary steps by which an overall chemical change occurs.
Concept #1: Reaction Mechanism Overview
Example #1: Consider the following reaction mechanism for the formation of nitrobenzene:
HNO3 (aq) + H2SO4 (aq) → H2NO3+ (aq) + HSO4– (aq)
H2NO3+ (aq) + C6H6 (aq) → C6H6NO2+ (aq) + H2O (l)
C6H6NO2+ (aq) + HSO4– (aq) → H2SO4 (aq) + C6H5NO2 (aq)
Identify the reaction intermediate(s) and catalyst(s).
Concept #2: Molecularity
Example #2: The elementary reaction, 2 NO2 (g) + F2 (g)2 NO2F (g) , is an example of a _____________ reaction.
Concept #3: Rate Law Determination
Example #3: Consider the following elementary steps. What is the rate law of the reaction mechanism?
N2O5 (g) ⇌ NO3 (g) + NO2 (g) [Fast]
NO2 (g) + N2O5 (g) → 3 NO2 (g) + O2 (g) [Slow]
NO3 (g) + O (g) → NO (g) + O3 (g) [Fast]
Practice: Consider the following elementary steps:
NO2 (g) + NO2 (g) → NO4 (g) + NO (g) [SLOW]
NO (g) + CO3 (g) → N (g) + CO4 (g) [FAST]
What is the rate law of the reaction mechanism?
Practice: The following reaction of 2 Br2 (g) + 2 NO (g) → N2 (g) + 2 Br2O (g) has the following rate law: Rate = k [Br2][NO]2. The proposed mechanism for the reaction is:
Br2 (g) + NO2 (g) → N (g) + Br2O (g) [SLOW]
N (g) + NO (g) → N2 (g) + O (g) [FAST]
O (g) + Br2 (g) → Br2O (g) [FAST]
Which of the following statements is/are false?
a) The rate determining step is bimolecular.
b) There are three elementary steps in the reaction mechanism.
c) The mechanism possesses a catalyst.
d) O is the only reaction intermediate in this reaction mechanism.
e) This is not a valid mechanism for the reaction.
