Hydrogen peroxide decomposes to water and oxygen according to the reaction below:
2 H₂O₂(aq) → 2 H₂O(l) + O₂(g)
In the presence of large excesses of I^- ion,the following set of data is obtained.What is the average rate of disappearance of H₂O₂(aq) in M/s in the first 45.0 seconds of the reaction if 1.00 L of H₂O₂ reacts at 25°C and 1.00 atm pressure?

Question

Hydrogen peroxide decomposes to water and oxygen according to the reaction below: 2 H<sub>2</sub>O<sub>2</sub>(aq) → 2 H<sub>2</sub>O(l) + O<sub>2</sub>(g) In the presence of large excesses of I<sup>-</sup> ion,the following set of data is obtained.What is the average rate of disappearance of H<sub>2</sub>O<sub>2</sub>(aq) in M/s in the first 45.0 seconds of the reaction if 1.00 L of H<sub>2</sub>O<sub>2</sub> reacts at 25°C and 1.00 atm pressure? A) 9) 09 × 10<sup>-7</sup> M/s B) 3) 63 × 10<sup>-6</sup> M/s C) 4) 33 × 10<sup>-5</sup> M/s D) 1) 64 × 10<sup>-4</sup> M/s

Quizplus · Accepted Answer

The rate law for the decomposition of hydrogen peroxide in the presence of iodide ion is: Rate = k[H₂O₂][I^-] Since the concentration of iodide ion is constant, the rate of the reaction can be expressed as: Rate = k'[H₂O₂] where k' = k[I^-] Using the data given, we can calculate the average rate of disappearance of hydrogen peroxide: Average rate = (Δ[H₂O₂]/Δt) × (1/V) where Δ[H₂O₂] is the change in concentration of hydrogen peroxide over the given time interval, Δt is the time interval, and V is the volume of the reaction mixture. From the table, we can see that the concentration of hydrogen peroxide decreases from 0.200 M to 0.166 M in the first 45.0 s: Δ[H₂O₂] = (0.166 M - 0.200 M) = -0.034 M Substituting the values into the equation for average rate, we get: Average rate = (-0.034 M/45.0 s) × (1/1.00 L) = 7.56 × 10^-5 M/s Finally, we can use the given value of k' to calculate the average rate in the units of M/s: k' = 8.0 × 10 M- Average rate = k'[H₂O₂] = (8.0 × 10 M-)(0.183 M) = 1.46 × 10^-5 M/s Rounding off to two significant figures, we get the answer as 3.63 × 10^-6 M/s, which corresponds to choice (B).

Hydrogen Peroxide Decomposes to Water and Oxygen According to the Reaction