The molar heats of combustion of C2H2,(g), C(graphite) and H2(g), are 310.62, 94.05, and 68.32 kcal respectively. Calculate heat of formation of C2H2.

We have to calculate2Cgraphite +H2(g)→C2H2(g);ΔH=?Given,C2H2(g)+5/2O2(g)→2CO2(g)+H2O(g)ΔH=−310.62kcalCgraphite +O2(g)→CO2(g);ΔH=−94.05kcalH2(g)+1/2O2(g)→H2O(g); ΔH=−68.32kcalMultiply Eq. (2) by Z and add in Eq. (3)2Cgraphite +2O2(g)→CO2(g); ΔH=−188.10kcalH2(g)+1/2O2(g)→H2O(g); ΔH=−68.32kcal=2Cgraphite +5/2O2(g)+H2(g)→2CO2(g)+H2O(g)ΔH=−256.42kcal … (4)Subtract Eq. (1) from Eq. (4) C2-H2(g)+5/2O2-(g)→2CO2  -(g)+H 2O-(g);ΔH=−310.6+2kcal--------------------------------------------------------------------------------------2Cgraphite +H2(g)→C2H2(g); ,              ΔH=+54.2kcal