I measured the change in pressure for the decomposition of hydrogen peroxide in the presence of a manganese(IV) oxide catalyst at 5 different temperatures:

$$\ce{2 H2O2 (l) ->[MnO2 (s)] O2 (g) + 2 H2O (l)}$$

Is there any way that I can find concentrations and then find the rate constant, $k$? And, using them, make an Arrhenius graph to find activation energy? Any help would be much appreciated.


Change in pressure was found using a Vernier Gas Pressure Sensor. The starting concentration of hydrogen peroxide was 3% or $\pu{0.88 mol}$. The starting pressure was always around $\pu{98kPa}$. The catalyst and hydrogen peroxide were mixed together after the stopper was put on the flask. The increasing pressure was measured and the highest it went to (at $\pu{70 ^\circ C}$) was around $\pu{145kPa}$.

Here is an example of what I have done so far to try and find the rate constant to plot on an Arrhenius graph:

At $\pu{303.15 K}$:

$\frac{P}{RT}= \frac{n}{v}$, which is the same as concentration.
$\frac{120.3}{8.314 \times 303.15} = \pu{0.477 mol dm-3}$
$\pu{0.477 mol dm-3}$ is the final concentration of oxygen created after $\pu{180s}$ had elapsed.
$\frac{\pu{0.477 mol dm-3}}{\pu{180 s}} = \pu{0.00265 mol dm-3 s-1}$
The ratio between oxygen and hydrogen peroxide is 1:2, therefore the rate at which hydrogen peroxide was depleted at is $\pu{0.0053 mol dm-3 s-1}$.

The ending concentration must be $\pu{0.88 M} - \pu{0.0053 mol dm-3 s-1} \times \pu{180 s} = -\pu{0.074 mol dm-3}$.

And this is where I think something has gone wrong... The pressure continued to increase even after this $\pu{180s}$ so I do not think the reaction went to completion.

I would then use the equation $k = \frac{\text{rate}}{\text{[final concentration hydrogen peroxide]}}$ to find $k$.

  • $\begingroup$ There is a way you can find the activation energy in this method. But, it is not the activation energy of original reaction. It'd be the reduced activation energy due to $\ce{MnO2}$ catalyst. $\endgroup$ Feb 26 at 4:46
  • $\begingroup$ Yes that is what I want to find. Thank you so so much for the clarification!! I do want to find the activation energy with the catalyst. How would I do that? How do I find the rate constant? @MathewMahindaratne I was thinking about somehow using P/(RT)=n/v which is the same as concentration but I do not know if that is even right or where to go from there $\endgroup$
    – HoneyBee
    Feb 26 at 15:49
  • $\begingroup$ I already voted to close your question due to lack of details. If you put some details including what you have done so far (e.g., how you find the change in pressure), I can reconsider my vote and decide to help you. $\endgroup$ Feb 26 at 16:00
  • $\begingroup$ Thank you I have made these edits and shown what I have done so far. @MathewMahindaratne $\endgroup$
    – HoneyBee
    Feb 26 at 20:40
  • $\begingroup$ Thanks for the addition. I retract my vote as promised and upvoted your effort. $\endgroup$ Feb 26 at 21:00

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