I am given the following

$\ce{H2O2 -> H2O + 1/2 O2}$ (catalysed by $\ce{KI}$)

There are two solutions. $[\ce{H2O2}]$ is the same in both solutions but $[\ce{I-}]$ is $\pu{0.01M}$ and $\pu{0.005M}$, respectively.

UV absorbance ($A$) is measured at $\pu{240 nm}$ at different times in a cell with depth $\pu{0.1 cm}$. $\varepsilon_{[\ce{H2O2}]} = \pu{35 M^{-1}cm^{-1}}$ at $\pu{240 nm}$. (Assume that the $A = 0$ in a solution without $\ce{H2O2}$)

The absorbance over time is:

Absorption data table

I am asked to determine the reaction order with respect to $\ce{H2O2}$ and $\ce{I-}$. I know that in order to determine the reaction order I should have the concentration of the components and plot that against time (in different ways to test all orders) and if the line is linear I have found the reaction order. However, I have never done this with a catalyst nor from absorbance which is why I am having a little trouble with understanding how to solve this.

I assumed that I should use Beer-Lambert's law ($A=\varepsilon c\ell$) somehow and from that calculate the concentration of $\ce{H2O2}$ but I don't have the absorbance to do so. And for $\ce{I-}$, I have the absorbance but not the molar absorbance coefficient to calculate the concentration.

I have tried to find examples or help online but failed to find anything like my problem so I would appreciate if someone could push me in the right direction of solving this problem. Thank you!


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