Hello, I'm writing a lab report for a Chem 2 "clock reaction" lab. and have hit a bit of a dillemma.
A quick summary of the lab:
The rate law for the following reaction was determined by doubling the initial concentrations of Hydroxide, iodide, and bromate ions in seperate trials.
the reactions contained a the same moles of thiosulfate ions which consumed the Iodine molecules, and added starch (which makes the solution turn black in the precence of Iodine molecules, so we could visually measure the time it took to reach the "indication point" with a stopwatch. The "indication point" was our method of comparison between the different trials containing different initial concentrations of the reactants.
After this part of the lab, we did more trials with the solution at different temperatures to determine the activation energy of the reaction and the frequency factor. Then we did a trial with a catalyst, which leads to my question.
1. Based on your results for the trial containing the catalyst, how does the catalyst effect the value of the activation energy of this reaction?
(I feel like the wording of this question is misleading).
In the presence of the catalyst, the reaction reached the "indication point" more quickly than the reaction without the catalyst. Therefore, the catalyst must either increase the number of effective collisions or decrease the activation energy. One way a catalyst could speed up a reaction is providing an alternate reaction path that has a lower activation energy, which increases the number of effective collisions of the reactant molecules without affecting the K value of the original, un-catalyzed reaction.
2. What additional experiment could you perform to determine the value of the activation energy for the catalyzed reaction?
a person could run multiple trials of the reaction including the catalyst at various temperatures. Plotting the rate constants in the form of ln (k) as a function of 1/T should allow us to calculate the value of the activation energy from the slope of the resulting line.
3. What is one possible difficulty you would face in performing the experiment that you described in your answer to the previous question? How Beowulf you overcome this difficulty?
A possible difficulty in performing the experiment described could be that the catalyzed reaction happens too quickly, making time measurements inaccurate. a way to relay the "indication point" would be to decrease the molarities of the reactants while keeping the concentration of the thiosulfate the same. Or, one could run the experiment only at low temperatures so that the reaction proceeds more slowly.
Is the answer to my last question acceptable? I can't ignore the feeling that I'm missing an important part of the conclusion. Why would the lab manual ask a question like this? (this is a community college science course btw).