Heat Capacity and Entropy of CoCl2 and MnCl2 from 11° to 300°K. Thermal Anomaly Associated with Antiferromagnetic Ordering in CoCl2

Abstract

The heat capacities of MnCl2 and CoCl2 have been measured between 11° and 300°K. By the use of the measurements of Murray on MnCl2 at lower temperatures the lattice and magnetic contributions to the heat capacity and entropy of MnCl2 have been evaluated. CoCl2 has a lambda peak in heat capacity at 24.71±0.05°K associated with the cooperative ordering of the magnetic moments of the cobaltous ions. The entropy change associated with this cooperative ordering is R ln2. Smooth values of the heat capacity, entropy, enthalpy, and free energy are tabulated at selected temperatures. The values of the entropy and enthalpy at 298.15°K are: MnCl2, S° = 28.26±0.05 cal deg—1 mole—1, H°–H0° = 3602±8 cal mole—1; CoCl2, S° = 26.09±0.05 cal deg—1 mole—1, H°–H0° = 3375±8 cal mole—1.