Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

Metaldehyde, $(\text{CH}_3\text{CHO})_4$, is employed as a solid fuel in camping stoves. The equation for metaldehyde’s complete combustion is given below. $(\text{CH}_3\text{CHO})_4(s) + 10\text{O}_2(g) \rightarrow 8\text{CO}_2(g) + 8\text{H}_2\text{O}(l)$ $\Delta H_c^{\circ}$ = standard enthalpy change of combustion. Which expression gives the correct value for the enthalpy change of formation of metaldehyde?

  • A$\Delta H_c^{\circ}\text{ metaldehyde} - (8\Delta H_c^{\circ}\text{ carbon} + 8\Delta H_c^{\circ}\text{ hydrogen})$
  • B$\Delta H_c^{\circ}\text{ metaldehyde} - (8\Delta H_c^{\circ}\text{ carbon} + 16\Delta H_c^{\circ}\text{ hydrogen})$
  • C$(8\Delta H_c^{\circ}\text{ carbon} + 8\Delta H_c^{\circ}\text{ hydrogen}) - \Delta H_c^{\circ}\text{ metaldehyde}$
  • D$(8\Delta H_c^{\circ}\text{ carbon} + 16\Delta H_c^{\circ}\text{ hydrogen}) - \Delta H_c^{\circ}\text{ metaldehyde}$

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