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### AuthorTopic: Kinetics of an (overall) negative 1st order reaction  (Read 2244 times) !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="https://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() {var po = document.createElement("script"); po.type = "text/javascript"; po.async = true;po.src = "https://apis.google.com/js/plusone.js";var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(po, s);})();

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#### AhBeng

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##### Kinetics of an (overall) negative 1st order reaction
« on: April 26, 2012, 03:36:57 AM »

Full Question : Qn8
http://www.rsc.org/images/2000_Rd%20_1_Questions_tcm18-190754.pdf

Thing is, I'm unable to obtain the value of k as 0.112 (the given answer).

My method :
Since order of reaction wrt to I3- is 1, and since
rate = c [I3ā]^1 where c = k [H3AsO3]^1 [H+]^-1 [Iā]^-2,
accordingly using c = ln2/t(1/2) (for any one of the 4 Runs) and substituting both the value of c, as well as the molarities of the other species (for that particular Run) into the equation
c = k [H3AsO3]^1 [H+]^-1 [Iā]^-2
we should be able to obtain the value of k, which based on the 4 Runs, are approximately 0.12 to 0.13 (to 2 sf), but the given answer is 0.11 (to 2 sf).

Any assistance would be much appreciated.
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#### Kemi

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##### Re: Kinetics of an (overall) negative 1st order reaction
« Reply #1 on: April 27, 2012, 05:20:50 AM »

I got 0.121 (a mean of the four ks, all cs calculated from linear fits). Maybe they mixed up two digits in the answer? Anyway, I wouldn't worry too much about such a small difference, because you can estimate the rate constant in different ways.

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#### AhBeng

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##### Re: Kinetics of an (overall) negative 1st order reaction
« Reply #2 on: April 27, 2012, 05:38:49 AM »