Determine reaction rate constant from the reaction time?

Question

I was doing some research and I came across an experiment similar to mine (potassium iodate with sodium bisulfite) from the University of Massachusetts (http://www.chem.umass.edu/genchem/chem122/122_Experiment_4.htm), but with the reaction of potassium permanganate with oxalic acid.

The rate equation is given as: Rate = k[KMnO4][H2C2O4].

It was stated that the value of k could be determined by dividing the concentration of the potassium permanganate [KMnO4] by the reaction time to find the rate and then dividing the rate by [KMnO4] multiplied by the concentration of the oxalic acid [H2C2O4] to find the reaction rate constant.

They provide the following equations:

Rate = [KMnO4]/t

k = Rate/([KMnO4][H2C2O4])

Would this be applicable to my reaction (potassium iodate with sodium bisulfite), because this would allow me to find the activation energy without performing trials to find k experimentally?

Answer 1

Assuming the reaction is a one step reaction, and does not have any elementary reactions, this could potentially work. However, if there are elementary reactions, this would change the rate law, and it would not be Rate = k[KIO3][NaHSO3]. You would also need to know the reaction order for both the potassium iodate and the sodium bisulfate, as well as the coefficients for both in the original reactions, yes you would be able to do this. Knowing the coefficients, you could figure out the rate using rate -dA/adT. You could plug this rate into the rate law, Rate = k[KIO3]^m[NaHSO3]^n. However, you would need to know the reaction orders for KIO3 and NaHSO3, to plug in for m and n, and these can only be determined experimentally. If you know these, however, this equation would work for you.