Neco Model Questions Vol1 2019 Chemistry Question 36

Element X and element Y are non‑metals in period 3. Their diatomic gases \(X_{2}\) and \(Y_{2}\) have standard enthalpies of formation of 0 kJ mol⁻¹. The most stable oxides have standard enthalpies of formation \(\Delta H_{f}^{\circ}(XO) = -285\) kJ mol⁻¹ and \(\Delta H_{f}^{\circ}(YO) = -320\) kJ mol⁻¹. The bond‑dissociation energies are \(D(X\!\! -\!\! X) = 250\) kJ mol⁻¹ and \(D(Y\!\! -\!\! Y) = 430\) kJ mol⁻¹. Assuming the oxide forms by the reaction \(X_{2}+\frac{1}{2}O_{2}\rightarrow XO\) (and similarly for Y), (i) calculate the net energy change \(\Delta E\) for the formation of one mole of XO and YO after the X-X or Y-Y bond is broken, and (ii) state which element forms the more thermodynamically favourable oxide.