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Topic: Determining Rate Laws  (Read 2077 times)

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Offline Ciubba

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Determining Rate Laws
« on: March 03, 2015, 05:35:44 PM »
I ran an experiment in which three reactants produced a colored gas. I varied the initial amount of one reactant while keeping the others constant and then measured how long it took for the absorption (of a complementary wavelength) of the gas to reach .7.

My question now is how do I determine the order?

If I knew the final amount rather than the initial amount, I could plot [A]=[A]0-kt , ln[A]=ln[A]0-kt. amd 1/[A]=1/[A]0+kt and see which plot looked linear, although that would only work for integer powers. Assuming that there is a graphical approach that would work for this situation, but it eludes me. Could someone point me in the right direction? I'm assuming that I can use that fact that A is the same (i.e. the amount of gas produced when absorption=.7) for all of the reactions.

Offline Borek

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Re: Determining Rate Laws
« Reply #1 on: March 04, 2015, 02:50:15 AM »
Start by making C vs time plots.
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Offline Ciubba

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Re: Determining Rate Laws
« Reply #2 on: March 04, 2015, 09:24:25 AM »
Start by making C vs time plots.

I've already done that, but my data are initial concentration until abs=.7 rather than the actual concentration at time t.

I could solve the most linear looking graph for A0 in the integrated rate law, but I'm not sure if that will work. In this case of 1/[A]0=1/[A]-kt it would imply that the y-intercept is actually 1/[A], but I don't believe that is accurate.
« Last Edit: March 04, 2015, 09:44:09 AM by Ciubba »

Offline Borek

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Re: Determining Rate Laws
« Reply #3 on: March 04, 2015, 01:50:28 PM »
Can you post these plots?
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Offline Ciubba

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Re: Determining Rate Laws
« Reply #4 on: March 04, 2015, 02:08:09 PM »
The left axis is initial concentration with whatever operation performed on it. So, the 1/[A]0 plot has y values of 1/[A]0. The x values are time in seconds until abs=.7.

http://s13.postimg.org/rf4qom7wl/boop.png
« Last Edit: March 04, 2015, 04:39:22 PM by Borek »

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