Partial molar volumes and heat capacities in (dimethylformamide + an n-alkanol)

Abstract

Densities and heat capacities divided by volume of (dimethylformamide + each of eight n-alkanols) (from methanol to n-octanol) have been measured over the complete mole-fraction range and converted into partial molar volumes and partial molar heat capacities for both components. Each partial molar quantity is a smooth function of the mole fraction. The excess partial molar volumes of the alkanols change gradually with composition and with the number of C atoms in the alkanol molecule from −1.2 cm 3 · mol −1 for methanol to +1.4 cm 3 · mol −1 for n-octanol. The partial molar volumes of dimethylformamide are distributed around its molar volume also in relation to the number of C atoms. The limiting values run from 74.74 cm 3 · mol −1 in methanol to 78.82 cm 3 · mol −1 in n-octanol. These results suggest a value in the hypothetical liquid HOH smaller than that in water. The excess partial molar heat capacities of the alkanols are small and predominantly negative. The values at infinitive dilution range from −1.7 J · K −1 · mol −1 for methanol to −8.7 J · K −1 · mol −1 for n-octanol. The partial molar heat capacity of dimethylformamide is close to its molar heat capacity down to a mole fraction of 0.2. At smaller mole fraction it becomes larger in methanol, ethanol, and n-propanol, and tends to lower values in the other alkanols.