The enthalpies of solution of REBr3 . nH(2)O(n=7 for RE=La, Ce, and Pr; n=6 for RE=Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Y) in aqueous KCl solution and those of KBr in aqueous RECl3 solution have been measured calorimetrically at 298.15+/-0.1 K. By means of a suitable thermochemical cycle, the standard molar enthalpies of formation for these twelve rare-earth bromide hydrates were obtained, and their lattice energies and dehydration enthalpies calculated. The corresponding data of REBr3 . 6H(2)O (RE-Pm, Er, Tm, and Lu) were estimated. The "double peak effect" during the property changes of the lanthanide elements and the probability that the effect will be applied for practice have been discussed.