Bottles of aqueous hydrogen peroxide, H2O2(aq)

CHEMISTRY · Multi-part · AP · Chemistry · Kinetics · Kinetics

Problem

Bottles of aqueous hydrogen peroxide, H2O2(aq), are often stored for months at room temperature even though the overall decomposition to water and oxygen is exergonic. 2 H2O2(aq)→2 H2O(l)+O2(g)ΔG298∘=−120 kJ mol−12\,\text{H}_2\text{O}_2(\text{aq}) \rightarrow 2\,\text{H}_2\text{O}(\text{l}) + \text{O}_2(\text{g}) \quad \Delta G^\circ_{298} = -120\,\text{kJ mol}^{-1} For the uncatalyzed reaction, the activation energy is Ea=76 kJ mol−1E_a = 76\,\text{kJ mol}^{-1}. (a) Describe what the negative value of ΔG298∘\Delta G^\circ_{298} indicates about the thermodynamic favorability of the decomposition reaction. (b) Explain—using kinetic reasoning—why a sealed bottle of hydrogen peroxide shows little observable decomposition at 298 K298\,\text{K} even though the reaction is thermodynamically favored. (c) Manganese(IV) oxide powder is sometimes added experimentally to a small sample of hydrogen peroxide, causing rapid bubble formation. Explain how the presence of MnO2 permits the reaction to proceed at a measurable rate without altering the overall thermodynamic favorability.

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