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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: DannyBoi on February 04, 2013, 05:39:36 PM

Title: Online drill exercises for calculating rate constants giving me incorrect answer
Post by: DannyBoi on February 04, 2013, 05:39:36 PM

Hi, I would like to know why I am always getting the incorrect answer when I input it into these online drill exercises:

http://mmotif.concordia.ca/teaching/

When I do the exercises for extracting rate constants from second-order reactions, I use the integrated rate law:

k = (1/[A]_t - 1/[A]₀) * 1/t

And after converting to the correct units, my answer is always exactly double the value of the "correct" answer. Can anyone say what the error is?

Title: Re: Online drill exercises for calculating rate constants giving me incorrect answer
Post by: Dirac on February 05, 2013, 12:22:32 AM

$$v=k[C]^{2}=-\frac{1}{2}\frac{d[C]}{dt}$$

remember:

$$aA\rightarrow pP$$

$$v=k[A]^{a}=-\frac{1}{a}\frac{d[A]}{dt}=\frac{1}{p}\frac{d[P]}{dt}$$