Answer:
The standard enthalpy of formation of methane is -67.2 kJ/mol.
Explanation:
[tex]C(s) \rightarrow C(g) \Delta H^o_{1,rxn} = 716 kJ/mol[/tex]...[1]
[tex]2H_2(g)\rightarrow 4H(g) ,\Delta H^o_{2,rxn} = 872.8 kJ/mol[/tex]...[2]
[tex]C(g)+4H\rightarrow CH_4, \Delta H^o_{3,rxn} =?[/tex]...[3]
Since, the bond formation is taking place energy will release that id reaction will be an exothermic reaction
[tex]\Delta H^o_{3,rxn} =4\times (-414 kJ/mol)=-1656 kJ/mol[/tex]
[tex]C(s)+2H_2(g)\rightarrow CH_4, \Delta H^o_{4,rxn} =?[/tex]...[4]
Using Hess's law:
[4] = [1] + [2] + [3]
[tex]\Delta H^o_{4,rxn} =\Delta H^o_{1,rxn} +\Delta H^o_{2,rxn} +\Delta H^o_{3,rxn} [/tex]
[tex]=716 kJ/mol+872.8 kJ/mol +(-1656 kJ/mol)=-67.2 kJ/mol[/tex]
The standard enthalpy of formation of methane is -67.2 kJ/mol.
