Is there a way to calculate values in the Arrhenius equation without a graphing calculator?
My Chemistry professor never mentioned anything about using graphing apparatuses, so
Just part A
This video confuses me, not to mention that I don't own a TI-85. I have a TI-84 Plus
My Chemistry professor never mentioned anything about using graphing apparatuses, so
Just part A
This video confuses me, not to mention that I don't own a TI-85. I have a TI-84 Plus
1 Answer
Well, you can do it on Excel, or by hand... You may want to take a look at this 10-minute video I made, which teaches you how to use Excel for Chemistry:
DISCLAIMER: LONG ANSWER! Lots of images.
Let's try an example... consider the following reaction.
https://kinetics.nist.gov/kinetics/Detail?id=1989NES/PAY5158-5161:1
https://kinetics.nist.gov/kinetics/Detail?id=1989NES/PAY5158-5161:1
The straight-line version of the Arrhenius equation is:
overbrace(ln k)^(y) = overbrace(-E_a/R)^(m) overbrace(1/T)^(x) + overbrace(ln A)^(b)
METHOD 1
Since you know that the activation energy is a constant with respect to a small enough temperature range, this should be a straight line if you plot
Once you calculate
When doing it by hand, you could pick the first and last data points, as it is a straight line... in doing so, estimate the slope:
=> "slope" = (Delta(lnk))/(Delta(1//T)) = (-26.7639 - (-27.361))/(0.002681 - 0.004348)
~~ -"358.19 K"^(-1)
The y-intercept will also be needed, and it is estimated by extrapolating back to
-"358.19 K"^(-1) = (ln A - (-27.361))/(0 - 0.004348)
=> "y-intercept" = ln A = -25.804
From here we should compare to the straight-line version of the Arrhenius equation:
ln k = -E_a/R 1/T + ln A
The slope then allows us to find the activation energy:
color(blue)(E_a) = -R cdot "slope"
= -8.314 cancel"J""/mol"cdotcancel"K" xx ("1 kJ")/(1000 cancel"J") xx -358.19 cancel("K"^(-1))
= color(blue)("2.98 kJ/mol")
The y-intercept allows us to find the frequency factor:
color(blue)(A) = e^("y-intercept")
= e^(-25.800)
= color(blue)(6.24 xx 10^(-12) "cm"^3"/molecule"cdot"s") or perhaps in units we are more familiar with... this is equal to
3.76 xx 10^9 "M"^(-1)cdot"s"^(-1) .
METHOD 2
Or, if you aren't that visual... on Excel, simply set up data columns like this:
Then select D3 through E9 and go to Insert > Recommended Charts > All Charts > X Y (Scatter).
You should get this:
With a little bit of formatting, you could get this:
And by right-clicking on the data point, go to Add Trendline, then scroll down to find and click "Display equation on chart" and "Display R-squared value on chart".
What you should end up with is:
From this we should again compare to the straight-line version of the Arrhenius equation:
ln k = -E_a/R 1/T + ln A
From this, the example slope is
-E_a/R = -"359.78 K"^(-1)
and the example y-intercept is
ln A = -25.798
Therefore, the activation energy is:
color(blue)(E_a) = -R cdot "slope"
= -8.314 cancel"J""/mol"cdotcancel"K" xx ("1 kJ")/(1000 cancel"J") xx -359.78 cancel("K"^(-1))
= color(blue)("2.99 kJ/mol")
and the frequency factor is:
color(blue)(A) = e^("y-intercept")
= e^(-25.798)
= color(blue)(6.25 xx 10^(-12) "cm"^3"/molecule"cdot"s") or perhaps in units we are more familiar with... this is equal to
3.77 xx 10^9 "M"^(-1)cdot"s"^(-1) .
We more-or-less got the same thing either way, so both ways work.