2 H2O2(aq) → 2 H2O(l) + O2(g) The decomposition of hydrogen peroxide to form water and oxygen gas is — Kinetics Chemistry Question
Problem Context
2 H2O2(aq) → 2 H2O(l) + O2(g)
The decomposition of hydrogen peroxide to form water and oxygen gas is represented by the equation above. A proposed mechanism for the reaction, which involves the free radicals HO• and HOO•, is represented by the three equations below.
H2O2 → 2 HO• (slow)
H2O2 + HO• → H2O + HOO• (fast)
HOO• + HO• → H2O + O2 (fast)
Model Answer
rate = k [H2O2]
One point is earned for the correct rate law.
Model Answer
(i) Time = 0.71 − 0.21 = 0.50 ± 0.05 hour
One point is earned for the correct time.
(ii) Time = 1.17 − 0.66 = 0.51 ± 0.05 hour
One point is earned for the correct time.
Model Answer
The data show that the time remains constant when the concentration of the reactant decreases by one-half, indicating that the reaction is first order.
The rate law for the proposed mechanism has [H2O2] to the first power, indicating a first-order reaction.
One point is earned for a correct explanation.
Model Answer
H2O2 + 2 OH− → O2 + 2 H2O + 2 e− 0.15 V
H2O2 + 2 e− → 2 OH− 0.88 V
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2 H2O2 → 2 H2O + O2 1.03 V
One point is earned for the correct value of E°.
Model Answer
ΔG° is less than 0.
ΔG° = −nFE°. Because E° is positive, ΔG° must be negative.
OR
E° is positive, thus the reaction is spontaneous. For spontaneous reactions, ΔG° is always negative.
One point is earned for the correct answer with justification.
Model Answer
(i) Only Ea should be circled. One point is earned for circling Ea and none of the other quantities.
(ii) Ea, the activation energy, is less for the catalyzed reaction than for the uncatalyzed reaction. A catalyst provides a new reaction mechanism that requires a lower minimum required potential energy for the reaction to occur. Thus the activation energy is lowered.
One point is earned for a correct answer with reference to an altered mechanism.