Thermodynamic study on the sublimation of six methylnitrobenzoic acids

• Published in: The Journal of chemical thermodynamics 2001-01, Vol.33 (1), p.103-112
• Main Authors: Monte, Manuel J.S., Hillesheim, Dorothea M.
• Format: Article
• Language: English
• Subjects: Chemical thermodynamics; Chemistry; Elements, mineral and organic compounds; enthalpies of sublimation; entropies of sublimation; Exact sciences and technology; General and physical chemistry; methylnitrobenzoic acids; standard Gibbs energies of sublimation; Thermodynamic properties; vapour pressures
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1006/jcht.2000.0729

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following six compounds: 2-methyl-3-nitrobenzoic acid, between T= 357.16 K and T= 371.16 K; 2-methyl-6-nitrobenzoic acid, between T= 355.16 K and T= 369.16 K; 3-methyl-2-nitrobenzoic acid, between T= 371.16 K and T= 385.14 K; 3-methyl-4-nitrobenzoic acid, between T= 363.21 K and T= 379.16 K; 4-methyl-3-nitrobenzoic acid, between T= 363.10 K and T= 377.18 K; 5-methyl-2-nitrobenzoic acid, between T= 355.18 K and T= 371.08 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, po= 105Pa, molar enthalpies ΔcrgHmo, entropies ΔcrgSmoand Gibbs energies ΔcrgGmoof sublimation at T= 298.15 K, were derived: