Energetic, Entropic, and Volumetric Effects in Nonaqueous Associated Solutions

On the basis of a simple two-state association model (TSAM), a comprehensive study of thermodynamic response functions for nonaqueous associated solutions is presented. The excess isobaric heat capacities CpE(T) and excess thermal expansivities VpE ≡ (∂VE/∂T)p for a number of alcohol–alkane, amine–alkane, alcohol–ether, and alcohol–alcohol mixtures have been experimentally determined at atmospheric pressure within 278.15–338.15 K for CpE and 283.15–333.15 K for VpE(T). A rich variety (in some cases unreported) of temperature dependences for CpE(T) but also for VpE(T) curves has been observed. This thermodynamic information has been rationalized with the TSAM, which is found to qualitatively account for all observations. Specifically, the model provides a detailed dissection of the energetic and entropic effects of association that are reflected on CpE(T), and of the volumetric effects that are echoed on VpE(T). The latter, almost unexplored to date, are found to be opposite to what is currently being conjectured for “low-temperature water”, and they stimulate further experimental studies on aqueous solutions of nonelectrolytes.