degmo
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Rate questions?
Hey guys,
I am stuck with this question. Can anyone help?
If I have a reaction mixture composed of:
20mL 4.0 M acetone
10mL 1.0 M HCL
20mL 0.0050 M I2
and if the reaction is zero order in I2, how long would it take for the I2 color to disappear?
Also if I have another mixture as follows:
20mL 4.0 M acetone
10mL 1.0 M HCL
20mL 0.0050 M I2
10mL H20
What is the initial concentration of H+ ion and I2?
Will the rate equation be something like this?
rate = K(acetone)^x(HCL)^y(I2)^0(H2O)^z
Thanks
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vulture
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Show us where you are stuck. We're not just going to solve this one for you without you putting any effort into it.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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degmo
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Hey Vulture,
For the first question, I know that the rate is calculated by the formula:
Rate=K(acetone)^m(HCL)^n
I just don't know how you can determine the time it takes for I2 color to disappear.
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GeneralChemTutor
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Is this the haloform reaction?
The reaction rate would probably include just the acid and acetone.
The time it takes for I2 to disappear is probably determined by the rate, which you need to figure out.
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unionised
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There isn't enough information to answer the question. Are you expected to try to find the rate constant from the literature?
IIRC the haloform reaction is base catalysed.
[Edited on 25-2-2004 by unionised]
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chemoleo
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Yes, I also thought one wouldnt be able to tell how long it would take for the I2 colour to disappear.
For one thing, the reaction will be some exponential decay process, according to v = e^(-kt), where k is the reaction constant.
Thus the reaction never really comes to an end. It would more sense to ask, when has 50% reacted and such.
Since you don't know the reaction constant - how could you tell?
Also what does it really mean if the reaction is zero order? Could you draw up the mechanism of the reaction?? Only then it would make sense to write
the reaction equation, with rate constants and such.
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Also if I have another mixture as follows:
20mL 4.0 M acetone
10mL 1.0 M HCL
20mL 0.0050 M I2
10mL H20
What is the initial concentration of H+ ion and I2? |
Well this should be easy if I am not mistaken. Shame on you guys that you didnt pick up on this! 
As both acetone and I2 are neutral (or so I believe), and HCl dissociates nearly 100%, the concentration of H+ (H3O+) would be
1M x 10/(20+10+20+10) = 166.67 mM!
- simply because none of the HCl has reacted, right at the beginning of the reaction!
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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unionised
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If the reaction is zero order in I2 then it will come to an end, its a linear decay, not exponential.
If the rate of loss of iodine were proportional to its concentration ie to [I2]^1 then it would be a first order reaction. If the rate were
proportional to [I2]^2 then it would be second order.
for a zero order reaction the rate is (and this is a bit odd) independent of the concentration of iodine.
(That said, zero order reactions are a bit uncommon. Metabolism of alcohol at moderate to large doses is one of the commonest ones).
Classically, the order of a reaction (found by experiment) was used to work out what the mechanism was; not the other way round.
Reaction order is an empirical measurement. The molecularity is a theoretical concept though it is commonly related to the order.
BTW Degmo, I meant are you meant to go and find the rate constant for this reaction in a data book or on the net or whatever and then use it.
Come to think of it, the question has so little data in it that I can answer it. The iodine will disapear on my birthday.
(If it looks like it will be early, I will cool it down and slow the reaction. If it seems like it will finish late I will warm it up. the temperature
was not specified)
[Edited on 1-3-2004 by unionised]
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