Hydrogen peroxide is a liquid at 298K. It is moderately stable under room conditions but will decompose quickly if a catalyst is added. reaction 1 2H2O2(l) → 2H2O (l) + O2 (g)

1. (a)(i)Define entropy.[1]
2. (a)(ii)Predict the sign of the standard entropy change of reaction 1. Explain your answer. sign explanation[1]
3. (b)Some bond energy data are shown in Table 3.1. Table 3.1 type of bond bond energy /kJmol⁻¹ O-O 150 O-H 460 O=O 496 Use the data in Table 3.1 to show that the enthalpy change of the following reaction is -196 kJ mol⁻¹. 2H2O2(g) → 2H2O(g) + O2(g)[1]
4. (c)Some standard entropies, Sº, are shown in Table 3.2. Table 3.2 substance Sº /J K⁻¹ mol⁻¹ H2O2(l) +102 H2O(l) +70 The enthalpy change and Gibbs free energy change for the following reaction are shown. 2H2O2(l) → 2H2O(l) + O2(g) ΔHº = –196 kJ mol⁻¹ ΔGº = –238 kJ mol⁻¹ Use the data given to calculate the standard entropy of oxygen, Sº, O2(g). Sº, O2(g) =[3]
5. (d)The decomposition of H2O2(aq) is catalysed by aqueous iron(III) chloride and by silver metal. Identify which of these two catalysts is acting as a homogeneous catalyst. Explain your answer. homogeneous catalyst explanation[1]
6. (e)The E values for two electrode reactions are given. H2O2 + 2H+ + 2e⁻ ⇌ 2H2O E° = +1.77V Cr3+ + e⁻ ⇌ Cr2+ E° = -0.41V
7. (e)(i)An electrochemical cell is constructed with the following half-cells (electrodes): • an acidified solution of H2O2, a platinum wire • Cr2+ mixed with Cr3+, a platinum wire. Identify the positive half-cell and calculate the standard cell potential, E°cell. positive half-cell E°cell =[1]
8. (e)(ii)Calculate the value of ΔGº for the cell reaction that occurs, per mole of H2O2. ΔGº =[2]
9. (f)The E values for two electrode reactions are given. H2O2 + 2H+ + 2e⁻ ⇌ 2H2O E° = +1.77V Co3+ + e⁻ ⇌ Co2+ Eº = +1.82V An electrochemical cell is constructed with the following half-cells. half-cell 1 an acidified solution of H2O2 under standard conditions, a platinum wire half-cell 2 a solution containing 0.020 moldm⁻³ Co³+ and 2.0 moldm⁻³ Co2+, a platinum wire
10. (f)(i)Use the Nernst equation to calculate the value of E, the electrode potential of half-cell 2 under these conditions. E[2]
11. (f)(ii)Write an equation for the cell reaction that occurs in this cell under these conditions.[1]
12. (g)(i)Define enthalpy change of hydration, ΔHhyd.[1]
13. (g)(ii)Aluminium fluoride, AlF3, is an ionic solid. Complete and label the energy cycle to show the relationship between: • the enthalpy change of solution of AlF3, ΔHsol • the lattice energy of AlF3, ΔHlatt • the enthalpy changes of hydration of Al3+ and F⁻, ΔHhyd Include state symbols for all substances and ions.[2]
14. (g)(iii)Relevant data for this question are given. ΔHsol AlF3 = -209 kJ mol⁻¹ ΔHhyd Al3+ = -4690 kJ mol⁻¹ ΔHhyd F⁻ = -506 kJ mol⁻¹ Use these data and your energy cycle in (g)(ii) to calculate the ΔHlatt of AlF3. ΔHlatt of AlF3 =[1]