Apparent molal heat capacities and volumes of pyridine and methyl-substituted pyridines in aqueous solution at 25°C

Abstract

We have made calorimetric measurements leading to apparent molal heat capacities of pyridine and four methyl-substituted pyridines in aqueous solution at 25.0°C. Measurements of densities of the same solutions have led to apparent molal volumes. The results are as follows: pyridine, φ ^°_C = 305.7 J−°K⁻¹-mole⁻¹ and φ ^°_V = 77.5 cm³-mole⁻¹; 2-methylpyridine, φ ^°_C = 370.0 J−°K⁻¹-mole⁻¹ and φ ^°_V = 94.3 cm³-mole⁻¹; 3-methylpyridine, φ ^°_C = 380.2 J−°K⁻¹-mole⁻¹ and φ ^°_V = 93.7 cm³-mole⁻¹; 4-methylpyridine, φ ^°_C = 378.9 J−°K⁻¹-mole⁻¹ and φ ^°_V = 94.3 cm³-mole⁻¹; 2,6-dimethylpyridine, φ ^°_C = 441.8 J−°K⁻¹-mole⁻¹ and φ ^°_V = 109.9 cm³-mole⁻¹. These φ ^°_C and φ ^°_V values are discussed in terms of effects of substitution of CH₃-for H− in the various solute molecules.