The heats of formation and combustion of 100 coal samples were estimated based on an additive method for coal. Analytical values of a database were processed to determine the structural properties of coal, such as the relation between C%-daf and the number of aromatic rings. The resulting equations of the relations of the indices of chemical structures of coal were applied to analytical data for coal samples to count the numbers of some interatomic bonds. The bond energy of aromatic carbons was estimated from the average bond energies of typical aromatic compounds. The bond energies of other types of interatomic bonds were cited from bond dissociation energies of simple compounds in the literature. Simple functional groups were allocated to coal samples, and the total enthalpy of the numbers of various bonds multiplied by the bond energy of each type of bond gave the total bond energy of coal. The total bond energy together with other thermodynamic data gave the enthalpies of formation and combustion of coal. The estimated enthalpy of combustion of coal was consistent with the measured enthalpy of combustion within +/- 5%.