No abstract

Expansion coefficients (a), thermal pressure coefficients (y), isothermal compressibilities, densities and heat capacities have been measured at 25 "C for pure components and the following mixtures : 1 -chloronaphthalene with the series of normal alkanes (n-C,) where n

For a pure substance, the spinodal curve is defined as the locus where thermodynamic quantities such as the thermal expansion coefficient a,, the isothermal compressibility KT, and the isobaric heat capacity C, are expected to diverge. Its location is of particular importance from both practical and theoretical points of view, since it represents the limit beyond which a particular state of matter, in our case the liquid state, can exist or not. In this work, several predictions of the spinodal curve have been tested, compared, and discussed for 2,3-dimethylbutane. Thecomparison with results found in the literature reveals that some conclusions established here could be of general application.

Apparent molar volumes ϕv have been measured for twelve alcohol/alkane mixtures between XOH = 0. 001 and 0. 2 at 298. 15 K. The systems studied were: methanol + n‐C6 ethanol and 1‐butanol + n‐C1, 1‐hexanol + n‐Cn with n = 6, 10, 12 and 16, 1‐heptanol + n‐C10, 1‐decanol + n‐Cn with n = 6, 10 and 16 and 1‐dodecanol + n‐C10 ϕv shows a sharp increase for XOH < 0. 05; values found at infinite dilute are several cm3/mol larger than the pure alcohol molar volume. Experimental results are compared with predictions from the Extended Real Associated Solution (ERAS) model which takes into account associational and physical effects as well as a reaction volume Δv* for hydrogen bond formation. Without any adjusted parameter the ERAS model gives good predictions for ϕv and the excess partial molar volumes at infinite dilution ΔV∞OH. It is found that, in the concentration region studied, the associational contribution dominates ϕv; the rapid fall of ϕv, with increasing alcohol concentration is due to alcohol self‐association and a corresponding increase in molecular cohesion. At infinite dilution, the associational contribution to ΔV∞OH. is nearly constant for all alcohols and hence the observed changes in ΔV∞OH values are almost entirely due to changes on the physical term. Experimental ΔV∞OH increase for a given alcohol as the chain length of the alkane increases and decrease for a series of increasingly longer 1‐alcohols in a given alkane. These changes are reproduced by the theory and explained in terms of differences in free volume between the two components as well as the associational contribution to ΔV∞OH.