In the reaction
S+32O2→SO3+2xkJ and SO2+12O2→SO3+ykJ
Heat of formation of SO2 is
x + y
x – y
2x – y
2x + y
S+32o2→SO3.....(1)ΔH1=−2x−kJ SO2+12O2→SO3....(2)ΔH2=−ykJ S+O2→SO2.....(3)ΔH3=zkJ
From Hess's law, ΔH3+ΔH2=ΔH1
z - y = -2x ∴ z = y - 2x
The heat of formation of SO2 is:
S+32O2→SO3+2x kJSO2+12O2→SO3+y kJ