Calculate the enthalpy of formation of solid PbO2 from solid lead and oxygen at 1 atm, from the following data at 298K. Pb (s) +  O2 (g) = PbO (s) H298 = -52.4 kcal 3 PbO (s) +  O2 (g) = Pb3O4 (s) H298 = -18.4 kcal Pb3O4 (s) + O2 (g) = 3 PbO2 (s) H298 = -22.7 kcal Ans.: Hf = -66.1 kcal/mole