# Homework Help: Need help help on reaction mechanism

1. May 25, 2009

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1. For the reaction

2NO + Cl2 --> 2NOCl

Match the appropriate rate law to each postulated mechanism.
A Rate = k[NO]2[Cl2]2
B Rate = k[NO][Cl2]
C Rate = k[NO][Cl2]2
D Rate = k[Cl2]
E Rate = k[Cl2]2
F Rate = k[NO]
G Rate = k[NO]2[Cl2]
H Rate = k[NO]2
I None of the above

NO + Cl2 --> NOCl2 slow
NOCl2 + NO ---> 2NOCl fast

2NO --> N2O2 slow
N2O2 + Cl2 --> 2NOCl fast

NO + Cl2 NOCl2 ---> fast equilibrium
2NOCl2 NOCl3 + NOCl ---> slow
NOCl3 ---> NOCl + Cl2 fast

NO + Cl2 ---> NOCl2 fast equilibrium
NOCl2 + NO ---> 2NOCl slow

i have no idea where to start. book isn't very helpful. basically, you look at the slow reaction then you subisitute the intermediate for the fast reaction. But i dont know what i do next. Do i cancel or what?

2. 5Br-(aq) + BrO3-(aq) + 6H+(aq) 3Br2(l) + 3H2O(l)

The above reaction is expected to obey the mechanism:

BrO3-(aq) + H+(aq) <-->HBrO3(aq) Fast equilibrium
HBrO3(aq) + H+(aq) <---> H2BrO3+(aq) Fast equilibrium
H2BrO3+(aq) + Br-(aq) <---> (Br-BrO2)(aq) + H2O(l) Slow
(Br-BrO2)(aq) + 4H+(aq) + 4Br-(aq) <---> products Fast

For each of the given rate expressions choose the correct expression for the rate constant (k)

-d[BrO3-]/dt
-d[Br-]/dt
-d[H+]/dt