Chapter 6: Energetic Effects in Hydrogen-bonded Liquids and Solutions

The heat capacity of a variety of liquids and solutions containing molecules that are able to form hydrogen bonds reflects energetic phenomena at a molecular level in a specific manner: its temperature dependence has the shape of a so-called Schottky peak which, in the light of simple statistical mechanical two-state models, indicates that the population of two particle energy levels prevails. We outline here that this simple scenario relating macroscopic and microscopic behavior is common to: hydrogen bonding in alcohols and other associated liquids and solutions; the anomalies of supercooled water; the thermodynamics of hydrophobic hydration; and the aggregation of the hydrophobic moieties of amphiphilic molecules in aqueous solution.