Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

Hess’s Law may be applied to find the average C-H bond energy in methane. $\Delta H^\circ_{at}$ = standard enthalpy change of atomisation, $\Delta H^\circ_f$ = standard enthalpy change of formation, $\Delta H^\circ_c$ = standard enthalpy change of combustion. Which data values are required to carry out the calculation?

  • A$\Delta H^\circ_{at}(\text{C}), \Delta H^\circ_{at}(\text{H}), \Delta H^\circ_f(\text{CH}_4)$
  • B$\Delta H^\circ_c(\text{C}), \Delta H^\circ_c(\text{H}_2), \Delta H^\circ_c(\text{CH}_4)$
  • C$\Delta H^\circ_c(\text{C}), \Delta H^\circ_c(\text{H}_2), \Delta H^\circ_f(\text{CH}_4)$
  • D$\Delta H^\circ_f(\text{CH}_4)$ only, as $\Delta H^\circ_f(\text{C})$ and $\Delta H^\circ_f(\text{H}_2)$ are defined as zero

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