C2H5OH(l)+3O2(g)⟶2CO2(g)+3H2O(l)ΔH=−1368kJ
2CO2(g)+3H2O(l)⟶C2H5OH(l)+3O2(g)ΔH=1368kJ.....(1)
C(s)+O2(g)⟶CO2(g)ΔH=−393.5kJ
2×[C(s)+O2(g)⟶CO2(g)ΔH=−393.5kJ]
2C(s)+2O2(g)⟶2CO2(g)ΔH=−787kJ.....(2)
H2(g)+12O2(g)⟶H2O(l)ΔH=−286.0kJ
3×[H2(g)+12O2(g)⟶H2O(l)ΔH=−286.0kJ]
3H2(g)+32O2(g)⟶3H2O(l)ΔH=−858.0kJ.....(3)
Adding eqn(1),(2)&(3), we have
2C(s)+3H2(g)+12O2(g)⟶C2H5OH(l)ΔH=−277
Hence the enthalpy of formation of ethyl alcohol is −277kJ.