Thermodynamic Studies on Melting Some α- and β-Derivatives of Naphthalene

Abstract

Methods for determining volume changes on melting have been briefly reviewed. A new apparatus has been described which is simple in operation, accurate in measurements and is free from some of the major limitations of the apparatuses used earlier. It has been used to determine volume changes on melting of α- and β-derivatives of naphthalene (C₁₀H₇X; X = NH₂, OH, COOH), as well as coefficients of cubical expansion of the solid compounds (α) and their melts (α'). The application of the apparatus has been extended to determine the densities of the compounds at any temperature both when entrapped air is present (d) and when it is completely absent (d'). An electrical method using a modified glass calorimeter has been employed for the measurement of latent heats of fusion, ΔH_f. From the experimentally determined values of ΔV_f/V_s,d', α and ΔH_f, the molar volume of the solid compound at the melting point (V₈), that of the melt at the melting point (V₁), the entropy of fusion (ΔS_f), the variation of the melting temperature with pressure [(∂T/∂P)_v] and the compressibility coefficient of the solid compounds (β) have been calculated and the results discussed.