The boundary curve of thermodynamic stability of the liquid phase on the basis of a generalised Berthelot's equation

A three-parametric modification of Berthelot's equation of state with an extra parameter n in the expression for the internal pressure (a generalised Berthelot's equation) was examined. The reduced form of this equation and formulae for the calculation of the spinodal were obtained. The spinodal of water was calculated. For a series of substances, the parameters of the spinodal at zero pressure and zero thermodynamic temperature were calculated. It was established that, in the region of positive pressures, the generalised Berthelot's equation describes the position of the spinodal on the phase diagram better than the generalised van der Waals equation, while preference is given to the generalised van der Waals equation in the region of negative pressures at low temperatures, since it gives an idea of the theoretical tensile strength of the liquid phase of a substance. Keywords : binodal, spinodal, Berthelot's equation, critical point, metastable liquid, negative pressure, theoretical tensile strength, van der Waals equation African Journal of Science and Technology Vol. 5(2) 2004: 1-8