[CHM 112] Kinetics Lab

[Andrew J. Pounds]

On 03/01/2015 09:23 PM, wrote:
>
> ​Hi, Dr. Pounds!
>
>
> I had a few questions on the lab.  I was wondering what the purpose of 
> finding the slope of the line was and if we would use that for any 
> other calculations.  Last lab we used it to find k, but it seems that 
> the values of k are the same for each trial and therefore would cancel 
> out to be 1 when put in the equation.  Is there a use for the slope or 
> am I missing something in the calculations?
>
>
> Thank you!
>
>

Whoa..  hold on there..



So you the lab description states "However, we won't actually measure 
the rate constant k.  Insteas we assume that since the concentration of 
reactants is the same in each trial, the measured rate is equal to k 
times some constant."

So you have the Arrhenius equation

$k = Ae^{-E_a/RT}$

the log of which is

$\ln k = \ln A - \frac{E_a}{R} \frac{1}{T}$

based on the statement from the lab, we are going to replace k with rate

$\ln \mathrm{rate} = \ln A - \frac{E_a}{R} \frac{1}{T}$

If we then plot the $\ln \mathrm{rate}$ on the y-axis and $\frac{1}{T}$ 
on the x-axis we should get a linear relationship with the slope equal 
to $-\frac{E_a}{R}$.  So from the slope you can determine the activation 
energy.

Got it?

\mathrm{rate}--
Andrew J. Pounds, Ph.D.  (pounds_aj at mercer.edu)
Professor of Chemistry and Computer Science
Mercer University,  Macon, GA 31207   (478) 301-5627
http://faculty.mercer.edu/pounds_aj

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