[gangst]

Hi,

I am posting as i am having difficulty calculating the activation energy of a reaction i have carried out. I have tried to using an arrhenius graph to calculate the activation energy, but have realised that instead of plotting log k against 1/T i have plotted log rate of reaction against 1/T.

I have never used the Arrhenius equation before, so sorry for my incompetence, and therefore I am having difficulty rearranging the equation to make Ea the subject.

I am going to post the data I am trying to use to calculate Ea. Iam really unsure of where I have gone wrong, rate of reaction increases with temperature as it should, however, log k values don't give me the negative correlation needed for an arrhenius plot.

is it possible to rearrange the equation to get the Ea value?



thanks for any help it is really appreciated.

[Valdorod]

gangst:

If you have data for the rate and concentration, you can plot the log(rate) vs log conc.  the slope of this curve gives you the order of the reaction.

rate = K[A]^p*c

from this you obtain

log(rate) = log K + p log[A] + log c

combining constants  you have

log (rate) = p log [A] + C which is in the form of y = mx + b

thus from the plot of log(rate) and log[A] you can find p

After you find p use

rate = K[A]^p to solve for k ( the rate constant)

k = rate/[A]^p

Now you can use the Arrhenius equation

k = A e^-Ea/RT

the linear form of this equation is

ln k = -Ea/R * 1/T + ln A : in y = mx + b

y = ln k

m = -Ea/R

x = 1/T

b = ln A

from you plot of ln k vs 1/T you can find Ea from the slope.

However, you do need at least three points, that is different k at different temp.

valdo

[gangst]

thanks for your help, i hadnt seen the relation between arrhenius and y = mx+ c, as excel had plotted by graph with a positive correation?!

iv sorted it now, thanks man!