Standard Gibbs energy of formation of Zn 8La determined by solution calorimetry and measurement of heat capacity from near absolute zero kelvin

Abstract

The thermodynamic properties of ZngLa were investigated by calorimetry. The standard entropy of formation at 298 K, Δ fS° 298, was determined from measuring the heat capacities, C p, from near absolute zero (2 K) to 300 K by the relaxation method. The standard enthalpy of formation at 298 K, Δ fH° 298, was determined by solution calorimetry in hydrochloric acid solution. The standard Gibbs energy of formation at 298 K, Δ fG° 298, was determined from these data. The results obtained were as follows: Δ fS° 298 (Zn 8La)/kJ·mol -1 = -297.18 ± 18; Δ fS° 298(Zn 8La)/J·mol -1·K -1 = -25.02± 3.60; Δ fG° 298 (Zn 8La)/kJ·mol -1 = -297.18 ± 18; The coefficient, γ, of the electronic term contributin to the heat capacity of Zn 8La was small, indicating that decrease of the density of states for 4f component of the lanthanum atom in the vicinity of E F. © 2006 The Japan Institute of Metals.