Thermodynamic properties of Na2W2O7(s) and Na2W4O13(s) in the temperature range 298.15–1000 K

The enthalpy increments Δ273.15 KTHm0 of Na2W2O7(s) and Na2W4O13(s) were measured in the temperature range 273–979 K by the drop method using a high temperature Calvet HT-1000 calorimeter. The results can be represented by the polynomial equations: Δ273.15 KTHm0(Na2W2O7)=−71,006+211.12T+10.720×10−2T2+2.566×106T−1Δ273.15 KTHm0(Na2W4O13)=−136,568+388.97T+6.643×10−2T2+6.950×106T−1 The expressions of the heat capacity against temperature for these two compounds were obtained from the differentiation of the above equations. By combining these results with data from the literature, smoothed thermodynamic functions have been calculated for Na2W2O7.