I am having trouble interpreting gas chromatography (GC) results for the production of ethyl acetate from acetic acid and ethanol. I am trying to find the reaction order from these results, as well as the proportionality constant $k_i = A_i/c_i$ for the relation between the $i$th peak area $A_i$ and corresponding concentration $c_i.$

I have the peak areas for each substance. I assume the corresponding concentrations are the arguments on the $y$-axis. With that I can get the proportionality constant $k_i$ for each analyte, but I'm failing to see how to calculate the reaction order from this.

Can I just ignore the proportionality constant $k_i$ and plot the three linear cases for the reaction orders to determine the order: $c$ vs $t$, $1/c$ vs $t$, and $\ln c$ vs $t$?


1 Answer 1


The problem has nothing to do with gas chromatography. It has to do with the kinetics of a chemical reaction.

Whatever the method used to get the concentrations, when you get the concentrations of the reactants (A, B, or C), you report them versus the time. The concentration of a reagent must decrease.

To analyze these results and get the order, you plot the logarithm of the concentration of A versus the time on a diagram. Look at the diagram ! Are the obtained points alined? If they are, the order of the reaction is $1$ with respect to A : the slope of the line joining the points is the 1st order rate constant. If the points are not alined, you should start again by plotting the inverse of the concentration of A versus the time. Here again the points should be alined. If they are, the reaction is $2$nd order with respect to A. If they are not alined, the order is not known. It is different from $1$ and from $ 2$. But it is not known yet.

  • $\begingroup$ I see, thank you!! If I may, I only have one more question just to make sure I get it, is the y-axis on the graph the concentration? Or do I need to do something else to get the concentration of each reactant? Thank you in advance $\endgroup$
    – pulsewidth
    Jun 11, 2023 at 21:00
  • $\begingroup$ The y-axis on the chromatogram is proportional to the concentration of the corresponding stuff. $\endgroup$
    – Maurice
    Jun 12, 2023 at 7:53

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