Problem: The methane molecule, CH4, has the geometry shown in following figure. Imagine a hypothetical process in which the methane molecule is "expanded," by simultaneously extending all four C–H bonds to infinity. We then have the process CH4(g) → C(g) + 4 H(g).Calculate the enthalpy change of formation of CH4(g)

FREE Expert Solution

We are asked to calculate the enthalpy change of formation of CH₄(g)

$\boxed{\mathbf{\Delta H}{\mathbf{°}}_{\mathbf{rxn}}\mathbf{=}\mathbf{\Delta H}{\mathbf{°}}_{\mathbf{f}\mathbf{,}\mathbf{ }\mathbf{product}}\mathbf{-}\mathbf{\Delta H}{\mathbf{°}}_{\mathbf{f}\mathbf{,}\mathbf{reactant}}}$

Note that we need to multiply each ΔH˚ by the stoichiometric coefficient since ΔH˚ is in kJ/mol. 

Balanced reaction :  C(s) + 2 H₂(g) →CH₄(g) .