[en] The heats of dilution of aqueous LaCl₃, PrCl₃, NdCl₃, SmCl₃, EuCl₃, GdCl₃, TbCl₃, DyCl₃, HoCl₃, ErCl₃, TmCl₃, YbCl₃, and LuCl₃ solutions have been measured up to saturation at 25⁰C. The integral heats of solution of LaCl₃ . 7H₂O, PrCl₃ . 7H₂O, NdCl₃ . 6H₂O, SmCl₃ . 6H₂O, EuCl₃ . 6H₂O, GdCl₃ . 6H₂O, TbCl₃ . 6H₂O, DyCl₃ . 6H₂O, HoCl₃ . 6H₂O, ErCl₃ . 6H₂O, TmCl₃ . 6H₂O, YbCl₃ . 6H₂O, and LuCl₃ . 6H₂O in water at 25⁰C have also been measured. The heat of dilution data are represented by empirical equations, and relative partial molal heat contents are calculated. The heat content trends across the rare earth chloride series are similar to the trends found for the rare earth perchlorate heat data, and can be correlated with a change in the inner sphere cation water coordination across the rare earth cation series. 11 figures, 3 tables, 43 references