
At 40°C, H2O2 (aq) will decompose according to the following reaction:
2H2O2(aq)→2H2O(l)+O2(g)
The following data were collected for the concentration of H2O2 at various times.
Times(s) | [H2O2](mol/L) |
0 | 1.000 |
2.16 × 104 | 0.500 |
4.32 × 104 | 0.250 |
a. Calculate the average rate of decomposition of H2O2 between 0 and 2.16 × 104 s. Use this rate to calculate the average rate of production of O2(g) over the same time period.
b. What are these rates for the time period 2.16 × 104 s to 4.32 × 104 s?
(a)

Interpretation: The decomposition reaction of H2O2 is given. The answers for each option using appropriate data from the given table are to be stated.
Concept introduction: The change observed in the concentration of a reactant or a product per unit time is known as the rate of the particular reaction. The differential rate law provides the rate of a reaction at specific reaction concentrations.
Answer to Problem 25E
Answer
The average rate of decomposition of H2O2 between 0 and 2.16×104 s is −2.31×10−5 mol/L⋅s_. The average rate of production of O2(g) between 0 and 2.16×104 s is 1.16×10−5 mol/L⋅s_.
Explanation of Solution
Explanation
Given
Concentration of H2O2 at 0 s is 1.000 mol/L.
Concentration of H2O2 at 2.16×104 s is 0.500 mol/L.
The reaction that takes place is,
2H2O2(aq)→2H2O(l)+O2(g)
The rate law for the above equation is written as,
Rate=−12Δ[H2O2]Δt=12Δ[H2O]Δt=12Δ[O2]Δt (1)
Where,
- Δ[H2O2] is the average rate of consumption of H2O2.
- Δ[H2O] is the average rate of production of H2O.
- Δ[O2] is the average rate of production of O2.
- Δt is the average time.
The average rate of decomposition of H2O2 between 0 and 2.16×104 s is calculated as,
Average Rate=Final concentration−Initial concentrationFinal time−Initial time
Substitute the values of concentration of H2O2 at 0 and 2.16×104 s in the above equation.
Average Rate=Final concentration−Initial concentrationFinal time−Initial time=(0.500−1.00) mol/L(2.16×104−0) s=−2.31×10−5 mol/L⋅s_
The average rate of decomposition of H2O2 between 0 and 2.16×104 s is −2.31×10−5 mol/L⋅s.
Substitute the above value in equation (1).
−12Δ[H2O2]Δt=12Δ[O2]ΔtΔ[O2]Δt=−12×(−2.31×10−5 mol/L⋅s)=1.16×10−5 mol/L⋅s_
Conclusion
The calculated average rate of decomposition of H2O2 between 0 and 2.16×104 s is −2.31×10−5 mol/L⋅s_. The average rate of production of O2(g) between 0 and 2.16×104 s is 1.16×10−5 mol/L⋅s_.
(b)

Interpretation: The decomposition reaction of H2O2 is given. The answers for each option using appropriate data from the given table are to be stated.
Concept introduction: The change observed in the concentration of a reactant or a product per unit time is known as the rate of the particular reaction. The differential rate law provides the rate of a reaction at specific reaction concentrations.
Answer to Problem 25E
Answer
The average rate of decomposition of H2O2 between 2.16×104 s and 4.32×104 s is −1.15×10−5 mol/L⋅s_. The average rate of production of O2(g) between 2.16×104 s and 4.32×104 s is 5.78×10−6 mol/L⋅s_.
Explanation of Solution
Given:
Concentration of H2O2 at 2.16×104 s is 0.500 mol/L.
Concentration of H2O2 at 4.32×104 s is 0.250 mol/L.
The reaction that takes place is,
2H2O2(aq)→2H2O(l)+O2(g)
The rate law for the above equation is written as,
Rate=−12Δ[H2O2]Δt=12Δ[H2O]Δt=12Δ[O2]Δt (2)
Where,
- Δ[H2O2] is the average rate of consumption of H2O2.
- Δ[H2O] is the average rate of production of H2O.
- Δ[O2] is the average rate of production of O2.
- Δt is the average time.
The average rate of decomposition of H2O2 between 0 and 2.16×104 s is calculated as,
Average Rate=Final concentration−Initial concentrationFinal time−Initial time
Substitute the values of concentration of H2O2 at 4.32×104 s and 2.16×104 s in the above equation.
Average Rate=Final concentration−Initial concentrationFinal time−Initial time=(0.25−0.500) mol/L(4.32×104 −2.16×104) s=−1.15×10−5 mol/L⋅s_
The average rate of production of O2(g) between 2.16×104 s and 4.32×104 s is 5.78×10−6 mol/L⋅s_.
The average rate of decomposition of H2O2 between 2.16×104 s and 4.32×104 s is −1.15×10−5 mol/L⋅s.
Substitute the above value in equation (2).
−12Δ[H2O2]Δt=12Δ[O2]ΔtΔ[O2]Δt=−12×(−1.15×10−5 mol/L⋅s)=5.78×10−6 mol/L⋅s_
Conclusion
The calculated average rate of decomposition of H2O2 between 2.16×104 s and 4.32×104 s is −1.15×10−5 mol/L⋅s_. The average rate of production of O2(g) between 2.16×104 s and 4.32×104 s is 5.78×10−6 mol/L⋅s_.
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