Van der Waals model and equation of state of nitrobenzene-alkanes solutions near the critical consolute temperature

On the basis of the fluctuation theory of phase transitions a system close to the critical point is the ideal gas of order parameter fluctuations. An extended equation of state for binary solutions close to the critical consolute temperature has been proposed taking into account the properties of a real Van der Waals gas in this model. This equation has been used to analyze the temperature dependences of the concentrations of a series of nitrobenzene + alkane binary solutions in terms of different order parameters. It has been shown that the molar concentration of the solution should be used as an order parameter of the analyzed systems. It has been determined that the parameters of the extended equation of state are linear functions of (a) the number of carbon atoms in alkanes and (b) the compressibility factor of the solution components.