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Ch.13 - Chemical KineticsWorksheetSee all chapters

# Reaction Mechanism

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Sections
Intro to Chemical Kinetics
Energy Diagrams
Catalyst
Factors Influencing Rates
Average Rate of Reaction
Stoichiometric Rate Calculations
Instantaneous Rate
Collision Theory
Arrhenius Equation
Rate Law
Reaction Mechanism
Integrated Rate Law
Half-Life

A Reaction Mechanism is a step-by-step sequence of elementary steps by which an overall chemical change occurs.

###### Understanding Reaction Mechanism

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) ⇌ NO(g) + NO(g)                                       [Fast]

NO(g) + N2O5 (g) → 3 NO2 (g) + O(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.