The following set of data was obtained by the method of initial rates for the reaction:
S₂O₈^2-(aq) + 3 I^-(aq) → 2 SO₄^2-(aq) + I₃^-(aq)
What is the initial rate when S₂O₈^2- is 0.15 M and I^- is 0.15 M?

Question

The following set of data was obtained by the method of initial rates for the reaction: S<sub>2</sub>O<sub>8</sub><sup>2-</sup>(aq) + 3 I<sup>-</sup>(aq) → 2 SO<sub>4</sub><sup>2-</sup>(aq) + I<sub>3</sub><sup>-</sup>(aq) What is the initial rate when S<sub>2</sub>O<sub>8</sub><sup>2-</sup> is 0.15 M and I<sup>-</sup> is 0.15 M? A) 4) 10 × 10<sup>-6</sup> M s<sup>-1</sup> B) 8) 10 × 10<sup>-3</sup> M s<sup>-1</sup> C) 1) 22 × 10<sup>-2</sup> M s<sup>-1</sup> D) 5) 40 × 10<sup>-2</sup> M s<sup>-1</sup>

Quizplus · Accepted Answer

The initial rate can be calculated by taking the initial concentrations of the reactants and dividing by the time it takes for the reaction to reach that rate. Since the concentrations of both S₂O₈^2- and I^- are both 0.15 M, we can assume they are the initial concentrations. To determine the initial rate, we need to observe the change in concentration of one of the reactants or products over time. Since we're given the method of initial rates, we can assume that we have observed the reaction at varying initial concentrations of the reactants and have recorded the corresponding initial rates. From this data, we can select two experiments where the initial concentration of one reactant is held constant while the initial concentration of the other reactant is doubled. We can then use the ratio of the two corresponding initial rates to determine the order with respect to the reactant whose concentration was doubled. Using the given reaction, we can see that the order with respect to S₂O₈^2- is 1 and the order with respect to I^- is 3. This means that when the concentration of I^- is held constant and the concentration of S₂O₈^2- is doubled, the initial rate will increase by a factor of 2. We can use this information and the given initial rate for the experiment where both concentrations are 0.15 M to solve for the initial rate when the concentration of S₂O₈^2- is 0.30 M and the concentration of I^- is 0.15 M: (initial rate for 0.15 M S₂O₈^2-)/(0.15 M S₂O₈^2-) = (initial rate for 0.30 M S₂O₈^2-)/(0.30 M S₂O₈^2-) (initial rate for 0.30 M S₂O₈^2-) = 2 × (initial rate for 0.15 M S₂O₈^2-) = 8 × 10^-3 M s^-1^-1 Therefore, the answer is B: 8)10 × 10^-3 M s^-1.

The Following Set of Data Was Obtained by the Method