Heat capacity, entropy, enthalpy, and Gibbs energy of 242PuF4 from 10 to 350 °K

Abstract

Heat capacity measurements have been made on a 20.9 g sample of 242PuF4 from 10 to 350 °K. The measurements from 20 to 350 °K were made by intermittent electrical heating with corrections based on the observed temperature drifts. Heat capacities determined in this way were compared with temperature drifts without electrical heating in the range 20 to 56 °K to evaluate the radioactive self-heating rate as (1.214±0.004) ×10−4 W/g Pu. From 10 to 20 °K heat capacities were obtained from this value of the radioactive self-heating rate and the temperature drifts without electrical heating. The heat capacity curve had the normal sigmoid shape. At 298.15 °K the heat capacity C°p, entropy S °, enthalpy H °−H °0, and tempered Gibbs energy (G °−H °0)/T are, respectively (116.19±0.29) J °K−1⋅ mole−1, (147.25±0.37) J °K−1⋅ mole−1, (22 385±56) J mole−1, and −(72.17±0.18) J °K−1⋅ mole−1. The changes in various thermodynamic functions for the formation of PuF6(g) from PuF4(c) and F2(g) are evaluated at 550 and 298.15 °K.