Find the enthalpy of formation for methane CH4 in kJkmol The

Find the enthalpy of formation for methane, CH4, in kJ/kmol. The lower heating value of methane is given as 50,016 kJ/kg at 298K.

Solution

1. C(s) + O2(g) CO2(g)..................................... H1 = –394 kJmol-1
2. 2H2(g) + O2(g) 2 H2O(g)............................. H2 = –572 kJmol-1
3. CO2(g) + 2 H2O(g) CH4(g) + 2 O2(g)........ H3 = +890 kJmol-1
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Eliminating oxygen, carbon dioxide, and water on both sides in all the three equations, we end up with:
Total: C(s) + 2 H2(g) CH4(g).............................H = –76 kJmol-1

Answer: The standard heat of formation for methane is –76 kJmol-1 or   –76000 kJkmol-1