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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.

See Also This Related BrainMass Solution

Rate Law mechanism observed

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

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

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

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

(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.

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
4. Step (2) is sufficiently slow that it can be considered rate-determining.

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