Enthalpy increments of Ba 2Te 3O 8(s) and Ba 3Te 2O 9(s) compounds

Abstract

The enthalpy increments of the compounds Ba 2Te 3O 8(s) and Ba 3Te 2O 9(s) were measured in the temperature range 298–965 K, using a high temperature Calvet calorimeter. The values were least square fitted in the following temperature dependent polynomial equations: Δ H 298.15 K T ( J/mol ) B a 2 T e 3 O 8 ( s ) = − 77 , 233 + 234.87 T + 0.08108 T 2 ( 298.15 – 862.8 K ) , Δ H 298.15 K T ( J/mol ) B a 2 T e 3 O 8 ( s ) = 21 , 533 − 209.39 T + 0.46007 T 2 ( 862.8 – 965 K ) , Δ H 298.15 K T ( J/mol ) B a 3 T e 2 O 9 ( s ) = − 116 , 177 + 338.96 T + 0.00741 T 2 + 4 , 310 , 572 T . The temperature differentials of the above equations gave the heat capacity equations for the respective compounds, which were compared with Neumann–Kopp's estimated heat capacities. As heat capacity of TeO 3 was not available in literature, it was estimated from that of TeO 2. Using the Gibbs energy of formation data of Ba 3Te 2O 9(s), reported in literature, Δ f H 298.15 K ° , and S 298.15 K ° of the compound were calculated as −2258 kJ/mol and 822 J/(mol K), respectively.