Mixing enthalpies of TbBr3-MBr liquid mixtures (M = Li, Na, K, Rb, Cs)

The molar enthalpies of mixing, < m i x H m in the binary liquid systems TbBr 3 -MBr (M = Li, Na, K, Rb, Cs) have been measured with a Calvet-type high-temperature microcalorimeter over the entire composition range with anaccuracy 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 TbBr 3 -LiBr system is positive in the TbBr 3 -rich region. For all the systems, the enthalpy minimum occurs at mole fraction x TbBr 3 0.3 - 0.4. The molar enthalpies of formation < f o r m H m (3MBr, TbBr 3 , 1) for M = Li, Na, K, Rb and Cs at 1113 K (arising from the reaction 3MBr ( 1 ) +TbBr 3 ( 1 ) = (3MBr, TbBr 3 ) ( 1 ) ) are found to be-4.8, -31.3, -63.3, -70.3 and -81.2 kJmol - 1 , respectively. The least-squares coefficients A, B, C, D and E in the equation A (kJ mol - 1 )=A+Bx+Cx 2 +Dx 3 +Ex 4 , where λ is an interaction parameter and x = x T b B r 3 , are also reported.