Gce Model Questions Vol1 2017 Chemistry Question 18

Metals A, B and C are aluminium (Al), zinc (Zn) and iron (Fe) respectively. Their standard reduction potentials are: Al^{3+}+3e^- \rightarrow Al E^{\circ}=-1.66\text{ V} Zn^{2+}+2e^- \rightarrow Zn E^{\circ}=-0.76\text{ V} Fe^{2+}+2e^- \rightarrow Fe E^{\circ}=-0.44\text{ V} (a) Rank the metals in order of decreasing reactivity towards dilute hydrochloric acid. (b) Using the standard enthalpies of formation (kJ mol^{-1}): \(\Delta_fH^{\circ}(\text{Al}_2\text{O}_3)=-1675\), \(\Delta_fH^{\circ}(\text{ZnO})=-350\), \(\Delta_fH^{\circ}(\text{Fe}_2\text{O}_3)=-824\), determine which metal forms the most thermodynamically stable oxide. (c) Calculate the enthalpy change for the reaction \(2\text{Al}+3\text{Cl}_2\rightarrow2\text{AlCl}_3\), given \(\Delta_fH^{\circ}(\text{AlCl}_3)=-704\text{ kJ mol}^{-1}\).