[bloomfieldboss]

Given the rate equation...
RATE = ([ Na2S2O3]/time) = k [I-]a [BrO3-]b [HCl]c
1A) You mix together in the proper manner the following:

    10.0 mL of .0100 M Potassium Iodide
    10.0 mL of .00100 M Sodium thiosulfate
    10.0 mL of water
    10.0 mL of .0400 M Potassium Bromate
    10.0 mL of .100 M HCl

The time to turn blue is... 100 sec

1B) You also mix together in the proper manner the following:

    10.0 mL of .0100 M Potassium Iodide
    10.0 mL of .00100 M Sodium thiosulfate
    10.0 mL of .0400 M Potassium Bromate
    20.0 mL of .100 M HCl

The time to turn blue is... 27 sec
Calculate:
The Experimental value of exponent c... 

Can someone please explain this to me?

[MuskieMan33]

If this is the iodine clock experiment, as it appears to be, we did a similar one in class. Needless to say, it was a huge failure for our entire class. Our reactions were supposed to be first order, but they looked like second order when graphed. Which would completely throw off all calculations. I thought it was a horrible experiment as nothing played out as it should have. Sorry I didn't help, but I'm just as lost as I could possibly be on the whole thing.

[Jasim]

This may help: http://www.chm.davidson.edu/vce/kinetics/MethodOfInitialRates.html

You'll first need to calculate the initial concentrations of your reactants.

I have a question relating to this, I know that experimental values such as these given can be used to calculate the rate constant 'k' and the coefficients a, b, and c. But isn't a, b, and c just the stoichiometric coefficients of the balance equation for the chemical reaction? Or is the coefficient the rate order of the reaction with respect to that specific reactant? And is there a difference?

[Cavillus]

This may help: http://www.chm.davidson.edu/vce/kinetics/MethodOfInitialRates.html

You'll first need to calculate the initial concentrations of your reactants.

I certainly agree, you need to calculate the real initial concentrations. However, it is easier to see that, in the second experiment, we add a double volume of HCl solution so, in the final mixture, his concentration is twice the one in the first kinetic study, while the time is reduced to 1/4. Reasoning this way, you can easily get the value for "c".

I have a question relating to this, I know that experimental values such as these given can be used to calculate the rate constant 'k' and the coefficients a, b, and c. But isn't a, b, and c just the stoichiometric coefficients of the balance equation for the chemical reaction? Or is the coefficient the rate order of the reaction with respect to that specific reactant? And is there a difference?

No, in general the exponents in kinetic relation and stoichiometric coefficients don't match, this happens only in one-step reactions.