Thermodynamics of lanthanide elements. III. Molar enthalpies of formation of Tb3+(aq), Ho3+(aq), Yb3+(aq), Yb2+(aq), TbBr3(cr), HoBr3(cr), and YbBr3(cr) at 298.15 K

Article abstract of DOI:10.1016/0021-9614(87)90065-6

Enthalpies of solution of high-purity terbium, holmium, and ytterbium metals and of the corresponding tribromides in aqueous hydrochloric acid of various molalities lead to the following standard molar enthalpies of formation Δ_fH_m⁰/(kJ * mol^-1) at 298.15 K: Tb3+(aq), -(698.3+/-1.5); Ho3+(aq), -(707.2+/-2.4); Yb3+(aq), -(670.5+/-2.7); Yb2+(aq), -(530.4+/-3.3); TbBr3(cr), -(839.1+/-2.4); HoBr3(cr), -(842.1+/-2.7); YbBr3(cr), -(793.8+/-2.4).A value of -(1.06+/-0.05) V is deduced from the above results for the standard potential of the reaction: Yb3+ + 1/2H2 = Yb2+ + H+, through the use of suitable entropy values.These results are discussed and compared with previous experimental or assessed values.