The heat capacity of natural lead molybdate (wulfenite, PbMoO 4 ) has been measured by the method of vacuum adiabatic calorimetry over the temperature range of (55 to 320) K, and its thermodynamic functions have been calculated. The obtained standard values are as follows:For extrapolation of heat capacity values to absolute zero, the equation C(T) ) (AT -1/Rβ + 1) -1/R has been used, where parameter R is the power at which the heat capacity verges toward the Dulong and Petit limiting value, and parameter β reflects structural anisotropy of the compound and can possess values from 1 to 3. The values of parameters found by means of linearization were R ) 0.61 and β ) 1.9. An error for the extrapolation data to absolute zero has been estimated based on the results of heat capacity measurements of the isostructural compound calcium tungstate, CaWO 4 . The values of the wulfenite heat capacity over the range of (0 to 55) K have also been calculated by the semiempirical method MNDO with the help of a program package on quantumchemical computation (MOPAC) and according to the method of interatomic potentials within the bounds of dynamics of crystal lattice theory using the computer program LADY.

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Measurements of the heat capacity of standard specimens of copper, benzoic acid, and heptane and their thermodynamic functions of molar heat capacity, change in entropy, and enthalpy have been carried out at a low-temperature thermal-physical installation in the temperature range (4.2 up to 320) K using the method of adiabatic calorimetry. The obtained data are in good agreement with the recommended values. The relative uncertainty limits of the calorimetric unit: ± 1.43 % at T = 5 K, ± 0.75 % at T = 10 K, ± 0.23 % at T = 40 K, and less than ± 0.11 % for the temperature range (90 up to 298.15) K have been determined according to the experimental data of measurements of the certified measure of oxygen-free electronic (OFE) grade copper heat capacity. According to the heptane heat capacity measurement, the values of its enthalpy and entropy of fusion at T fus = 182.54 K, ΔH fus = (14047 ± 19.6) J·mol−1 and ΔS fus = (76.96 ± 0.11) J·mol−1·K−1, have been determined. These values are also in a satisfactory agreement with the reference data.

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