Thermodynamic study of Cs3Na(MoO4)2: Determination of the standard enthalpy of formation and standard entropy at 298.15 K

The enthalpy of formation at 298.15 K and low temperature heat capacity of Cs3Na(MoO4)2 have been measured for the first time in this work using solution calorimetry and thermal-relaxation calorimetry in the temperature range T = (1.9-299.6) K, respectively. The solution calorimetry measurements, performed in 2 M HNO3 solution, have yielded an enthalpy equal to ΔrHm(298.15 K) = (6.79 ± 1.72)  kJ·mol−1 for the reaction:3/2Cs2MoO4(cr)+1/2Na2MoO4(cr)=Cs3Na(MoO4)2(cr)Combining with the enthalpies of formation of Cs2MoO4(cr) and Na2MoO4(cr), also determined in this work in 0.1 M CsOH and 0.1 M NaOH solutions, respectively, the standard enthalpy of formation of Cs3Na(MoO4)2 at 298.15 K has been determined as ΔfHmo(Cs3Na(MoO4)2, cr, 298.15 K) = −(2998.5 ± 3.0) kJ·mol−1. The heat capacity and entropy values of Cs3Na(MoO4)2 at 298.15 K have been derived as Cp,mo(Cs3Na(MoO4)2,cr,298.15K)=(296.3±3.3) J·K−1·mol−1 and Smo(Cs3Na(MoO4)2,cr,298.15K)=(467.2±6.8) J·K−1·mol−1. Combining the newly determined thermodynamic functions, the Gibbs energy of formation of Cs3Na(MoO4)2 at 298.15 K has been derived as ΔfGmo(Cs3Na(MoO4)2,cr,298.15K)=-(2784.6±3.4) kJ·mol−1. Finally, the enthalpies, entropies and Gibbs energies of formation of Cs3Na(MoO4)2 from its constituting binary and ternary oxides have been calculated.