THERMODYNAMIC PROPERTIES OF PYRIDINE .1. VAPOR-PRESSURES, HIGH-TEMPERATURE HEAT-CAPACITIES, DENSITIES, CRITICAL PROPERTIES, DERIVED THERMODYNAMIC FUNCTIONS, VIBRATIONAL ASSIGNMENT, AND DERIVATION OF RECOMMENDED VALUES

Measurements leading to the calculation of standard thermodynamic prop erties for pyridine (Chemical Abstracts registry number 110-86-1) are reported for temperatures from the triple-point temperature T-tp=231.5 1 K to T=560 K. The standard state is defined as the ideal gas at the pressure p=p degrees=101.325 kPa. Vapor pressures were measured by com parative ebulliometry for the pressure range 5 kPa to 270 kPa (tempera ture range: T=319 K to T=426 K). Two-phase (liquid + vapor) heat capac ities were measured for the temperature range 300 <(T/K) < 580 with a differential scanning calorimeter (d.s.c.), and saturation heat capaci ties C-sat were derived. Densities for the liquid phase were measured for the temperature range 323 ( (T/K) < 523. The critical temperature T-c was determined experimentally by d.s.c., and the critical pressure acid critical density were derived. Enthalpies of vaporization were c alculated. Literature values for enthalpy increments and entropies by adiabatic heat-capacity calorimetry for the temperature range 10 < (T/ K) < 360 and the molar energy of combustion were combined with the pre sent results to derive standard entropies, enthalpy increments, and Gi bbs free energies of formation at temperatures between T-tp=231.51 K a nd T=560 K. A new assignment of the fundamental vibrational wavenumber s for pyridine is reported. Comparisons with standard entropies calcul ated statistically provide corroboration for the calorimetrically deri ved values. The results are used to test the effectiveness of several common vapor-pressure formulations in the representation of broad pres sure ranges. (C) 1996 Academic Press Limited