The standard enthalpy of formation ( H_f^ ) at 298 K for methane, CH_4(g) , is -74.8 kJ mol^-1 . The additional information required to determine the - Chemistry MCQ AIEEE 2006 2026 | ExamTest.live

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The standard enthalpy of formation (Δ H_{f}^{\circ}) at 298 K for methane, CH_{4} (g), is - 74.8 kJ mol^{- 1} . The additional information required to determine the average energy for C - H bond formation would be:

A $the dissociation energy of H_{2} and enthalpy of sublimation of carbon$
B $latent heat of vapourization of methane$
C $the first four ionization energies of carbon and electron gain enthalpy of hydrogen$
D $the dissociation energy of hydrogen molecule, H_{2}$

Solution & Step-by-step Explanation

The enthalpy of formation of methane is for the reaction: C (graphite) + 2 H_{2} (g) \to CH_{4} (g) To calculate the C - H bond energy, we need the enthalpy of the reaction in the gaseous state: C (g) + 4 H (g) \to CH_{4} (g) This requires:Sublimation of Carbon: C (graphite) \to C (g) Dissociation of Hydrogen: H_{2} (g) \to 2 H (g) With these, we can use Hess's law to find the energy released when four C - H bonds are formed.

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The standard enthalpy of formation (Δ H_{f}^{\circ}) at 298 K for methane, CH_{4} (g), is - 74.8 kJ mol^{- 1} . The additional information required to determine the average energy for C - H bond formation would be:

the dissociation energy of H_{2} and enthalpy of sublimation of carbon

latent heat of vapourization of methane

the first four ionization energies of carbon and electron gain enthalpy of hydrogen

the dissociation energy of hydrogen molecule, H_{2}

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