The combustion reaction can be written as follows,
C3H8(g)+5O2→3CO2+4H2O;ΔH=−2220.0kJmol−1
Cgraphite+O2(g)→CO2(g);ΔH=−393.5kJmol−1
H2(g)+21O2(g)→H2O(l);ΔH=−285.8kJmol−1
Now, the formation reaction of propane is
3C(graphite)+4H2(g)→C3H8(g)ΔHf=3ΔHC∘(graphite)+4ΔHC∘(H2(g))−ΔHC∘(propane)ΔHf=3×(−393.5)+4×(−285.8)−(−2220)=−103.7kJmol−1