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The standard enthalpy of formation ( ∆ H f ∘ ) at 298  K for methane, CH 4 ( g ) is -74.5  kJ / mol . The additional information required to determine the average energy for C - H bond dissociation would be ________.

Options

  1. Athe dissociation energy of H 2 and enthalpy of sublimation of C
  2. Blatent heat of vaporization of methane
  3. Cthe first four ionisation energies of carbon and electron gain enthalpy of hydrogen
  4. Dthe dissociation energy of H 2 molecule

Correct answer

A. the dissociation energy of H 2 and enthalpy of sublimation of C

Step-by-step solution

Chemical equation corresponding to formation of methane is : C ( graphite ) + 2 H 2   → CH 4 ( g )     ∆ H f ∘ = - 74 . 5   kJ / mol Enthalpy change of any reaction can be written in terms of bond energy: ∆ H = ∑ Bond   energy   of   reactants - ∑ Bond   energy   of   products ∆ H f ∘ = ( Sublimation   energy   of   graphite + 2   ( B . D . E ) H - H ) - ( 4 × ( B . D . E . ) C - H ) B . D . E

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