An equation of state describing hydrophobic interactions.

Several thermodynamic properties for the process of dissolution of pure hydrocarbons into water are found to be linearly related to the number of hydrogens on the hydrocarbon molecule. From the correlations found for the Gibbs energy change, enthalpy change, and heat capacity change, along with the use of an average minimum solubility temperature, an equation of state for the hydrophobic effect is derived. The entropy change upon dissolution per hydrocarbon hydrogen atom is close to -R ln 2. A model based upon a "tetrahedrally" localized water molecule with one corner defined by a carbon-hydrogen group and the other three corners defined by water molecules is used to estimate the observed entropy and heat capacity changes.