Using bond energy data, calculate heat of formation of isoprene5Cs+4H2g→H2C=C|CH3−C|H=CH2Given, C-H = 98.8 kcal, H-H 104 kcal           C-C = 83 kcal C=C - 147 kcal and C(s) → C(g) = 171 kcal

ΔHReaction = Bond energy data released for formation of bond + Bond energy data used for dissociation of bondΔHReaction =2(C−C)+2(C=C)+8(C−H)+5Cs→g+4H−H=[2×83+2×147+8×98.8]+[5×171+4×104]=+20.6kcal