Apparent molar isentropic compressions - A critical commentary

The definition of apparent molar isentropic compressions of solutes in solution is rigorously examined. The equation conventionally used to calculate these properties using isentropic compressibilities of solutions and solvent is misleading. The approach originally described by Harned and Owen in 1958 is shown to have merit. These authors defined an isentropic molar property of solutes, identifed here as phi(K-sj; prac), which is not the apparent molar isentropic compression, -[partial derivative phi(V-j)/partial derivative p](s) The difference is a function of the molality of the solute together with the densities and isobaric heat capacities of solvent and solution.