Determination of thermodynamic function of the Rb–Te(IV)–O system using DSC

Abstract

The standard molar heat capacity measurements on compounds Rb2TeO3 (s), Rb2Te2O5 (s) and Rb2Te4O9 (s) in the Rb–Te(IV)–O system were taken using differential scanning calorimeter in the temperature range 325–675 K. The compounds were synthesized by solid-state route and characterized using X-ray diffraction technique. The molar heat capacity values were least squares analyzed, and the dependence of the molar heat capacity with temperature can be given as, $$ \begin{aligned} C^{\text{o}}_{\text{p,m}} \left( {{\text{Rb}}_{2} {\text{TeO}}_{3} , \, s,T} \right) \, /{\text{J K}}^{ - 1} {\text{mol}}^{ - 1} & = 156.00 + 0.02 \, \left( {T/{\text{ K}}} \right){-}4.12 \times 10^{6} \left( {T \, /{\text{K}}} \right)^{ - 2} \\ C^{\text{o}}_{\text{p,m}} \left( {{\text{Rb}}_{2} {\text{Te}}_{2} {\text{O}}_{5} , \, s,T} \right) \, /{\text{J K}}^{ - 1} {\text{mol}}^{ - 1} &= 216.50 + 0.03 \, \left( {T/{\text{ K}}} \right){-}2.52 \times 10^{6} \left( {T \, /{\text{K}}} \right)^{ - 2} \\ C^{\text{o}}_{\text{p,m}} \left( {{\text{Rb}}_{2} {\text{Te}}_{4} {\text{O}}_{9} , \, s,T} \right) \, /{\text{J K}}^{ - 1} {\text{mol}}^{ - 1} &= 351.80 + 0.04 \, \left( {T/{\text{ K}}} \right){-}3.52 \times 10^{6} \left( {T \, /{\text{K}}} \right)^{ - 2} \\ \end{aligned} $$ From these data, thermodynamic functions such as enthalpy increment (H T o − H 298.15 o ), entropy (S T o ) and Gibbs energy functions (fef) were evaluated.