Question

Question(s):

Answer 1

In an aqueous solution, you have the iodide reacting with hypochlorite ion to form hypoiodite and chlorine ions and is supposed to follow the following mechanism:

\(step~1\): \(\sf OCl^- + H_2O \rightarrow \rightleftharpoons HOCl + OH\) (FAST)
where k\(_1\) is the forward reaction and k\(_{-1}\) is the reverse reaction.

\(step ~2\): \(\sf I^- + HOCl \rightleftharpoons HOI + Cl^-\) (slow, equilibrium)
k\(_2\) is the forward reaction

\(step~3\): \(\sf HOI + OH^- \rightleftharpoons H_2O + IO^-\) (fast, equilibrium)

1. Which of the following isn't true?

A. molecularity of each step is 2
B. the limiting step is step 2
C. chloranol is the only reaction intermediate
D. the reaction is a complex reaction
E. All true

2. What is the overall rate equation of the reaction?

@Kainui @empty

Answer 2

i could possible have a go at question 2 with the rate equation. thats just kinetics with multiple reactions but not sure about 1

Answer 3

@chris00 Molecularity is the number of reactants for a reaction, it's what the numbers in SN2 or E1 stand for.

The limiting step is the slow step, everything happens quickly, pretty straightfoward there I think.

C appears to be the answer, because hydroxide as well as several others are also reaction intermediates since it appears on both sides, if you write the overall chemical equation by adding these all up you'll see they cancel cause it appears once on the left and right, you get \[OCl^- + I^- \leftrightharpoons OI^- + Cl^-\] Everything else is a reaction intermediate. (Not to be confused with a transition state, which is usually a transient intermediate which might look like carbon with 5 bonds or something)

The reaction isn't a complex one. I am not sure what exactly this term means but I looked it up and it looks like it specifically refers to reactions with catalysts or some weird stuff going on.

Answer 4

but what is the catalyst though..

Answer 5

i remember last semester how we determined overall rate equation with catalysis and catalytic reactors, but i'm having trouble understanding what the catalyst is.

Answer 6

Not sure if my knowledge in chemical reaction engineering is useful here since I'm unsure what the catalyst is

Answer 7

because if we are talking about the rate limiting step etc, wouldn't we have an adsorption, surface reaction and desorption reactions?

Answer 8

Well there isn't a catalyst here it looks like.

Answer 9

I guess this makes the overall rate equation difficult. Like i can find the overall net equation to the first step and well since step 2 isn't really a parallel reaction then its kinda hard to link it in

Answer 10

I basically just googled complex reaction and looked at this and then closed it lol http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Complex_Reactions

I think we can go more in depth however for this question (part 2) when he's asking for the overall rate equation it's really just going to be dependent on the slow step, which is basically why they call it "the rate determining step" or at least that's what my gen chem teacher is saying in the back of my mind to me right now.

So I would just say the overall rate is (assuming it's an elementary reaction):

\[k_2 [I^-] [HOCl]\]

Answer 11

like if we consider the first reaction:

\[r _{net_1}=r _{forward}+r _{reverse}\]
\[-r _{forward}=k _{1}C _{OCL ^{-}}C _{H _{2}O}\]
Therefore,

\[r _{forward}=-k _{1}C _{OCL ^{-}}C _{H _{2}O}\]

Now,

\[r _{backwards}=k _{-1}C _{HOCL}C _{OH}\]

Thus net reaction equation for step 1 is

\[r _{net}=-k _{1}C _{OCL ^{-}}C _{H _{2}O}+k _{-1}C _{HOCL}C _{OH}\]

Answer 12

like i could solve for catalysis and enzyme reactions, but this reaction isn't really anything like that

Answer 13

There are no enzyme or catalysts here though yeah, but we could combine all the rate laws together I'm not too familiar with that haven't done it in a while but basically looks like you're doing the right thing, beats me.

Answer 14

you could do it separately but i don't think thats answering the question ahah

Answer 15

Yeah I wish I had that book with me, but I left it at home, it talks about combining the rates together and stuff like this in some depth oh well. What kinda chemistry questions are you into I gotta review I have my chemistry GRE tomorrow so I gotta study I guess.

Answer 16

i have my elements of chemical reaction engineering book with me but it doesn't delve into any reactions like this. more bioreactors and enzymatic reactions. :/

Answer 17

Yeah like Michaelis-Menten and all that and Burke-Lineweaver plots it couldn't hurt for me to check that out again or whatever, that's totally likely stuff to end up on the test

Answer 18

YEP!

Answer 19

I can't believe what i studied was useful haha

Answer 20

Hahaha is it useful? I haven't ever used it but I've not really done much with proteins and junk. Can you explain what they're like or how you've used them I'm curious haha

Answer 21

well it really isn't useful in this reaction though... :/

Answer 22

Yeah forget this reaction I just have to study the entirety of under grad chemical knowledge haha

Answer 23

they are used to show competitive, uncompetitive and non-competitive reversible inhibition in enzymatic reactions.

but yeah has no relevance though hahaha

Answer 24

i think they are used to show how inhibitors affect the rate of reaction

Answer 25

only for enzymatic catalysed reactions though

Answer 26

Oh fancy I vaguely remember there being like 3 or so rules like that let you shift where it intercepts the y-axis or x-axis or something haha

Answer 27

yeah! you just see if the slope of the intercept changes and from there you can determine if its one of those inhibition types

Answer 28

but never really interested me much to go learn about it more than what we had to know about them and how to draw the graphs..

Answer 29

i only really enjoy kinetics in reaction engineering even though I've done until 3rd year chemistry is that it involves a lot of maths. Its pretty fancy stuff

Answer 30

like using design equations to solve tank geometry, volume concentration etc

Answer 31

anyway, i'm going out for dinner. I'm enthused if there is a solution to this when i come back!

Answer 32

Awesome that sounds cool. I'm curious, like are you using a lot of linear algebra to design tanks? That sounds pretty interesting.

Answer 33

More calculus than linear algebra, although linear algebra is used to some degree. You can always give this a read:

Elements of Chemical Reaction Engineering - H. Scott Fogler.

Very insightful which links chemistry into processing chemicals though reaction kinetics and tank design etc