Methanol is widely considered as a potential alternative fuel

CHEMISTRY · Multi-part · A Level · Chemistry · Energetics · Energetics

Problem

Methanol is widely considered as a potential alternative fuel. A measured enthalpy change for its complete combustion in the gas phase at 298 K is CH3OH(g)+32O2(g)→CO2(g)+2H2O(l),  ΔH=−726 kJ mol−1CH_3OH(g) + \frac{3}{2}O_2(g) \to CO_2(g) + 2H_2O(l),\; \Delta H = -726\,\text{kJ mol}^{-1} The following standard molar enthalpies of formation are known at 298 K: CO2(g),  −393.5 kJ mol−1CO_2(g),\; -393.5\,\text{kJ mol}^{-1} H2O(l),  −285.8 kJ mol−1H_2O(l),\; -285.8\,\text{kJ mol}^{-1} O2(g),  0.0 kJ mol−1O_2(g),\; 0.0\,\text{kJ mol}^{-1} No direct ΔHf∘\Delta H_f^\circ value for CH3OH(g)CH_3OH(g) is given. (1) Part 1: (a) Confirm that the combustion equation above is balanced with respect to both atoms and charge. (2) Part 2: (b) Using the information provided, determine the standard molar enthalpy of formation, ΔHf∘\Delta H_f^\circ, of CH3OH(g)CH_3OH(g). Show all reasoning and intermediate steps. (3) Part 3: (c) Account for the sign and magnitude of the value obtained in part (b) in terms of the relative strengths of bonds broken and bonds formed during the hypothetical formation of CH3OH(g)CH_3OH(g) from the elements in their reference states.

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