Add time:09/07/2019         Source:sciencedirect.com

The vapor pressure of scandium trifluoride is measured using a calibrated Knudsen effusion mass spectrometer. The vapor pressure of ScF3 (s) between 1159 and 1411 K is log10P (atm) = {−(17774 ± 85)T} + (8.698 ± 0.068)The vaporization enthalpy and entropy are 81.3 ± 0.4 kcal mol−1 and 39.8 ± 0.3 cal K−1 mol−1 respectively at 1275 K. The present vapor pressures give a second-law value ΔH° (298.15 K) of 85.2 ± 2.8 kcal mol−1 for the reaction ScF3 (s) = ScF3 (g) . The corresponding third-law value is Δ°(298.15 K) = 89.7 ± 2.7 kcal mol−1, computed using an estimated value of S° (298.15 K) for ScF3 (s) of 23.4 ± 2.0 cal K−1 mol−1. A selected thirdlaw vaporization enthalpy, ΔH°(298.15 K) = 89.9 ± 2.7 kcal mol−1, and Δf°(298.15 K) =-295.3 ± 3.1 kcal mol−1 for ScF3 (g) reported in the literature give Δunf°(298.15 K) = −385.2 ± 4.1 kcal mol−1 for ScF3 (s) . This result is compared with enthalpies of formation obtained from calorimetric and e.m.f. measurements and with values derived from previously reported vapor pressure results.

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