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# Kinematics: Rate Law and Rate Constant

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Consider the reaction of peroxydisulfate ion S2O8 ^2 - with iodide ion (I-) in aqueous solution:
S2O8^2-(aq) + 3I-(aq)  2SO4 ^2-(aq) + I3-(aq)
At a particular temperature the initial rate of disappearance of S2O8^2- varies with reactant concentrations in the following manner:
Experiment [S2O8 2-] (M) [I-] (M) Initial Rate (M/s)
1 0.018 0.036 2.6 × 10-6
2 0.027 0.036 3.9 × 10-6
3 0.036 0.054 7.8 × 10-6
4 0.050 0.072 1.4 × 10-5

(a) Determine the rate law for the reaction and state the units of the rate constant.
(b) What is the average value of the rate constant for the disappearance of S2O8^2- based on the four sets of data?
(c) How is the rate of disappearance of S2O8^2- related to the rate of disappearance of I-?
(d) What is the rate of disappearance of I- when S2O8^2- =0.025M and [I-] = 0.050 M?

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