Thermodynamic study on the sublimation of six methylnitrobenzoic acids |
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| Affiliation: | 1. Centro de Investigação em Química, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal;2. Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA;1. Department of Chemical and Materials Engineering, National Central University, Taoyuan, 32001, Taiwan;2. Department of Chemical Engineering, National Taiwan University, Taipei, 10617, Taiwan |
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| Abstract: | 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: |
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