C(graphite)+O2(g)→CO2(g)H=−393.5kJ................1
C(graphite)+1/2O2(g)→CO(g) ΔfH⊖ CO.......................2
and
CO+1/2O2(g)→CO2(g) ΔcH⊖ CO.......................3
From these equations, it can be seen that
ΔfH⊖ CO = ΔcH⊖(graphite)−ΔcH⊖(CO)
During complete combustion of one mole of butane, 2658 kJ of heat is released. The thermochemical reaction for above change is (a) 2C4H10(g)+13O2(g)→8CO2(g)+10H2O(l); ΔcH=−2658.0kJ mol−1 (b) C4H10(g)+132O2(g)→4CO2(g)+5H2O(l); ΔcH=−1329.0kJ mol−1 (c) C4H10(g)+132O2(g)→4CO2(g)+5H2O(l); ΔcH=−2658.0kJ mol−1 (d) C4H10(g)+132O2(g)→4CO2(g)+5H2O(l); ΔcH=+2658.0kJ mol−1