Mixing enthalpy of TbCl₃-MCl liquid mixtures (M = Li, Na, K, Rb, Cs)

The molar enthalpies of mixing, Δ_mixH_m in the binary liquid systems TbCl₃ - MCI ( M = Li, Na, K, Rb, Cs ) have been measured with a Calvet - type high temperature microcalorimeter over the entire composition range with an accuracy of about 6%. Mixing of the two liquid components was achieved by using the “break-off ampoule technique”. All the investigated systems show negative enthalpies of mixing with a minimum value of approximately -2.4, -9.9, -20.5, -26.0 and -28.8 kJ mol^-1, for M = Li, Na, K, Rb and Cs, respectively occuring at nearly the same molar fraction of TbCl₃, x_TbCl3 ≈ respectively, at X_TbCl3 ~0.4. The molar enthalpies of formation Δ_formH_m (3MCl,TbCl₃,l) for M = Li, Na, K at 1109 K and for M = Rb and Cs at 1175 K, arising from the reaction 3MCl_(l) + TbCl_3(l) = (3MCl,TbCl₃)_(l) are found to be -9.6, -36.1, -72.6, -87.4 and -97.6 kJ mol^-1, respectively. The least-squares coefficients A, B, C, D in the equation λ (kJmol^-1)= A + Bx + Cx² + Dx³ where λ is an interaction parameter are also reported.