A Semi-Empirical Equation for the Vapor Pressure of Liquids as a Function of Temperature

Abstract

The slight reverse curvature in the plot of logP versus 1/T (P, vapor pressure; T, absolute temperature) may be explained on the basis of the nonideal behavior of the vapor together with the change in heat of vaporization with temperature. If it is assumed that ΔH is linear with T and that the van der Waals a/V2 term is a first approximation to the deviation from the ideal, the following equation may be obtained by integration of the Clapeyron equation: logP=A+BT+C logT+DPT2.The last term is the nonideal gas correction with constant D=a/2.303R2. With constants A, B, and C determined empirically, the equation reproduces experimental vapor pressures from the triple point to the critical point with an average deviation of 0.3 percent.

Vapor pressures of isopropyl, t-butyl and 2-chloroethyl benzoates at reduced pressures.

“…The polynomial with four parameters is equivalent The Antoine equation is; \n(P)= Aa-BJ(t+ Ca) (7) or t\n(P)=Aat+Da-Ca\n(P) (8) where Da=AaCa-Ba. As the relations between pressure and temperature in Eqs.…”

Phase equilibria from the exactly integrated Clapeyron equation

“…are, of course, particular forms of equation (21)-as already pointed out, at least in part, by Mosselman et al (2) -while the empirical equations of Graetz (57) and Frost-Kalkwarf, (88) ln (21) and p is the experimental vapour pressure at the same temperature. Legend: curves obtained from equation (21).…”

Élaboration des lois d'état d'un liquide et de sa vapeur pour les modèles d'écoulements diphasiques

“…Les expressions de ces courbes sont nombreuses dans la littérature [13]. Citons par exemple celle proposée par Frost et Kallkwarf [14], utilisée pour décrire les courbes de saturation de certains hydrocarbures :…”