# Similar Reaction Mechanisms

#### OmiChem

I'm given two reaction mechanisms, both are supposedly for the same reaction and I'm asked to prove it. The reaction mechanisms are:

#1

OCl- + H2O --> HOCl + OH- (medium speed)
HOCl + I- --> HOI + Cl- (slow)
HOI + OH- --> H2O + OI- (fast)

#2

OCl- + H2O --> HOCl + OH- (slow speed)
HOCl + I- --> ICl + OH- (medium)
ICl + 2OH- --> OI- + Cl- + H2O (fast)

I'm guessing that since the original reactants are the same for both and they both form OI- and water as a product, they are the same.. the only difference I can see is that the chlorine ion is separated in a different step, which causes a difference in the rate of that elementary reaction. Also, the rate expression for the final reaction: Rate = k[I-] SHOULD be right, but i'm not sure if it is.. I- seems to be the ion that affects the rate but I'm a little behind on my organic chem so I need some help...thx ahead of time

#### Gokul43201

Staff Emeritus
Gold Member
You are required to prove that they pertain to the same overall reaction ?

In both cases, find the net reaction by simply adding the parts. What do you get ?

#### OmiChem

Oh, sorry, i should of explained more.. there are three parts to the question.. the first is to show that both are for the same reaction, I should of known that, sorry slipped my mind totally to use the net equation... wow lol. Other than that, I am given the rate expression and asked questions about changes such as tripling the I- concentration and such, i do not need help with that. It then proceeds to ask me which mechanism is correct. This i dont understand. How do i figure out which of the mechanisms is correct...if both are for the same reaction, aren't they both correct?

#### Gokul43201

Staff Emeritus
Gold Member
No, they won't both be correct. I can make up a bogus mechanism for the same reaction, and it would definitely be wrong. You determine the correct mechanism by looking at the rate equation. According the the opening post, Rate = k[I-] is the given rate equation.

What do you know about rate determining steps ?

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