Research: Science and Education
On the Clausius–Clapeyron Vapor Pressure Equation S. Velasco,* F. L. Román, and J. A. White Departamento de Física Aplicada, Universidad de Salamanca, 37008 Salamanca, Spain; *
[email protected] To provide the temperature dependence of the saturated pressure, P, of a fluid along the liquid–vapor coexistence curve, most chemistry and physics textbooks use the Clausius– Clapeyron equation (1–8) P 1 1 ln A (1) P0 T0 T where P0 and T0 are the vapor pressure and the absolute temperature of a reference point in the coexistence curve and A is a constant characteristic of the substance. Equation 1 is usually derived from integration of the Clapeyron equation for vaporization,
% vap H dP dT T Vv Vl
(2)
under the following assumptions: (i) the molar enthalpy (latent — ≈ constant), (ii) the heat) of vaporization is constant (∆vap H molar volume of the liquid is negligible respect to the molar — l
