Standard Gibbs Energy of Formation of Zn₈La Determined by Solution Calorimetry and Measurement of Heat Capacity from Near Absolute Zero Kelvin

Abstract

The thermodynamic properties of Zn₈La were investigated by calorimetry. The standard entropy of formation at 298 K, Δ_fS₂₉₈^°, 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_fH₂₉₈^°, was determined by solution calorimetry in hydrochloric acid solution. The standard Gibbs energy of formation at 298 K, Δ_fG₂₉₈^°, was determined from these data. The results obtained were as follows: Δ_fH₂₉₈^°(Zn₈La)/kJ·mol⁻¹ = −297.18±18; Δ_fS₂₉₈^°(Zn₈La)/J·mol⁻¹·K⁻¹ = −25.02±3.60; Δ_fG₂₉₈^°(Zn₈La)/kJ·mol⁻¹ = −289.71±18. The coefficient, γ, of the electronic term contributing to the heat capacity of Zn₈La was small, indicating that decrease of the density of states for 4f component of the lanthanum atom in the vicinity of E_F.