EQUATION OF STATE OF COMPRESSED LIQUIDS - STATISTICAL-MECHANICAL BASIS

Recent advances in the statistical-mechanical theory of equilibrium fluids can be used to obtain an equation of state for compressed liquids, thereby supplying a theoretical basis for a century of empiricism. The empirical results, dating back to P. G. Tait, essentially state that the isothermal bulk modulus (reciprocal of the isothermal compressibility) of a liquid is nearly linear in the pressure, with the slope being a function of temperature only. The present theory includes supercritical fluids and low-density vapors, and so gives more complicated mathematical expressions than the empirical formulas, but the numerical results are almost the same. This point is illustrated for both computer simulations and real fluids. The theory shows that supercritical fluids do not approach liquid-like behavior until the pressure is roughly 50 times the critical pressure.