The standard molar enthalpies of formation, Delta H-f(m)0 (298.15 K) of Pb2Fe2O5(s) and PbFe5O8.5(s) have been determined using acid solution calorimetry. The enthalpies of solution of the compounds Pb2Fe2O5(s) and PbFe5O8.5(s), as well as those of mixtures of Fe2O3(s) and Pb3O4(s) in HCl (aq, 6 mol.dm(3)) at 298.15 K were measured. Using these values, the standard enthalpies of formation (Delta H-f(m)0) of Pb2Fe2O5(s) and PbFe5O8.5(s) were determined as -(1324.2 +/- 11.1) kJ.mol(1) and -(2347.8 +/- 10.7) kJ.mol(1), respectively. (C) 2012 Elsevier Ltd. All rights reserved.