Standard Gibbs Energy of Formation of Zn<SUB>8</SUB>La Determined by Solution Calorimetry and Measurement of Heat Capacity from Near Absolute Zero Kelvin

Abstract

The thermodynamic properties of Zn 8 La were investigated by calorimetry. The standard entropy of formation at 298 K, Δ f S 298 , was determined from measuring the heat capacities, Cp, from near absolute zero (2 K) to 300 K by the relaxation method. The standard enthalpy of formation at 298 K, Δ f H 298 , was determined by solution calorimetry in hydrochloric acid solution. The standard Gibbs energy of formation at 298 K, Δ f G 298 , was determined from these data. The results obtained were as follows: Δ f H 298 (Zn8La)/kJ·mol -1 =-297.18 ±18; Δ f S 298 (Zn 8 La)/J·mol -1 ·K -1 = -25.02±3.60; Δ f G 298 (Zn 8 La)/kJ·mol -1 =-289.71 ± 18. The coefficient, γ, of the electronic term contributing to the heat capacity of Zn 8 La was small, indicating that decrease of the density of states for 4f component of the lanthanum atom in the vicinity of E F .