Mixing Enthalpies of TbBr3-MBr Liquid Mixtures (M = Li, Na, K, Rb, Cs)

Abstract

The molar enthalpies of mixing, ΔmixHm in the binary liquid systems TbBr3-MBr (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 -1.25, -8.3, -17.0, -20.0 and -22.5 kJ mol-1, for M = Li, Na, K, Rb and Cs, respectively. The mixing enthalpy in the TbBr3-LiBr system is positive in the TbBr3-rich region. For all the systems, the enthalpy minimum occurs at mole fraction xThBr3 ≈ 0.3 - 0.4. The molar enthalpies of formation ΔformHm (3MBr, TbBr3, 1) for M = Li, Na, K, Rb and Cs at 1113 K (arising from the reaction 3MBr(1) +TbBr3(1) = (3MBr, TbBr3)(1)) are found to be -4.8, -31.3, -63.3, -70.3 and -81.2 kJ mol-1, respectively. The least-squares coefficients A, B, C, D and E in the equation λ (kJ mol-1) = A + Bx + Cx2 + Dx3 + Ex4, where λ is an interaction parameter and x = xTbBr3, are also reported.