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Rate Law for Proposed Mechanism

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Consider the reaction 2NO(g) + O2 ---> 2NO2 (g). The following mechanism has been proposed to explain the experimental rate law:
1. 2NO --> and <-- N2O2 (fast)
2. O2 + N2O2 --> 2NO2 (slow)

Give the rate law for the proposed mechanism. If necessary, use the pre-equilibrium assumption to determine an expression for the concentration(s) of any intermediate(s) that may appear in the derived rate law.

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Solution Preview

Since step 2 is the rate-determining step, the rate law is
rate = k2[N2O2][O2]...(1)
Now, we need to ...

Solution Summary

This solution includes calculations for finding the required rate equation.

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See Also This Related BrainMass Solution

Rate Law mechanism observed

The rate law for the Br—- catalyzed reaction
Br-
C6H5NH2 + HNO2 + H+ C6H5N2+ + 2H2O

is observed to be rate = = k [H+][HNO2][Br -].

A proposed mechanism is
k1
(1) H+ + HNO2 H2NO2+ (rapid equilibrium)
k-1

k2
(2) H2NO2+ + Br- NOBr + H2O (slow)

k3
(3) NOBr + C6H5NH2 C6H5N2+ + H2O + Br- (fast)

Deduce the rate law for this mechanism and relate the observed rate constant k to the rate constants appearing in the assumed mechanism.

Notes:
1. Step (1) is a rapid equilibrium, meaning k1 and k-1 are much faster than k2.
2. The forward and reverse rates are equal for step (1) since it is an equilibrium; this fact can
be used to get an expression for the concentration of the intermediate H2NO2+.
3. Recall, the reaction orders for elementary reactions are determined by the reaction
stoichiometry.
4. Step (2) is sufficiently slow that it can be considered rate-determining.

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