THE HEAT-CAPACITY AND DERIVED THERMODYNAMIC FUNCTIONS OF LA2SI2O7 ANDCE2SI2O7 FROM 4 TO 1000 K

The heat capacities of cerium and lanthanum silicates (Ce2Si2O7 and La 2Si2O7) were measured from 4 to 400 K by adiabatic calorimetry. The de rived thermodynamic functions, {H degrees(T)-H degrees(0}, S degrees a nd {G degrees-H degrees(0)}/T were calculated. The standard molar entr opies at 298.15 K were determined as 220.32+/-0.44 J mol(-1) K-1 and 2 10.7+/-0.42 J mol(-1) K-1, respectively.Enthalpy increments relative t o 298.15 K were measured by drop calorimetry from 500 to 900 K. From t hese data the thermodynamic functions, including the enthalpy and Gibb s free energy of formation of the two compounds were derived for tempe ratures up to 1000 K.