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

Abstract

The enthalpy of formation at 298.15 K and low temperature heat capacity of Cs 3 Na(MoO 4 ) 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 HNO 3 solution, have yielded an enthalpy equal to Δ r H m (298.15 K) = (6.79 ± 1.72) kJ · mol −1 for the reaction: 3 / 2 Cs 2 MoO 4 ( cr ) + 1 / 2 Na 2 MoO 4 ( cr ) = Cs 3 Na ( MoO 4 ) 2 ( cr ) Combining with the enthalpies of formation of Cs 2 MoO 4 (cr) and Na 2 MoO 4 (cr), also determined in this work in 0.1 M CsOH and 0.1 M NaOH solutions, respectively, the standard enthalpy of formation of Cs 3 Na(MoO 4 ) 2 at 298.15 K has been determined as Δ f H m o (Cs 3 Na(MoO 4 ) 2 , cr, 298.15 K) = −(2998.5 ± 3.0) kJ · mol −1 . The heat capacity and entropy values of Cs 3 Na(MoO 4 ) 2 at 298.15 K have been derived as C p , m o ( Cs 3 Na ( MoO 4 ) 2 , cr , 298.15 K ) = ( 296.3 ± 3.3 ) J · K −1 · mol −1 and S m o ( Cs 3 Na ( MoO 4 ) 2 , cr , 298.15 K ) = ( 467.2 ± 6.8 ) J · K −1 · mol −1 . Combining the newly determined thermodynamic functions, the Gibbs energy of formation of Cs 3 Na(MoO 4 ) 2 at 298.15 K has been derived as Δ f G m o ( Cs 3 Na ( MoO 4 ) 2 , cr , 298.15 K ) = - ( 2784.6 ± 3.4 ) kJ · mol −1 . Finally, the enthalpies, entropies and Gibbs energies of formation of Cs 3 Na(MoO 4 ) 2 from its constituting binary and ternary oxides have been calculated.