Heat Capacity of NiF2 from 12 to 300°K. Thermodynamic Functions of NiF2. The Thermal Anomaly Associated with the Antiferromagnetic Ordering

Abstract

The heat capacity of NiF₂ has been measured calorimetrically between 12 and 300°K. There is an anomaly in heat capacity rising to a maximum of 9.23 cal deg^—1 mole^—1 at 73.22°K. The anomaly is associated with the antiferromagnetic ordering of the magnetic moments of the nickel ions. Values of heat capacity, entropy, enthalpy, and free energy are tabulated at selected temperatures. The entropy at 298.16°K is 17.59±0.04 cal deg^—1 mole^—1. For the reaction NiF₂+H₂=Ni+2HF, ΔH₀⁰=29.56±0.20 kcal and ΔH⁰=30.06±0.20 kcal at 298.16°K.