Objective of this experiment is to determine the saturation temperature for various pressures of a pure substance and to calculate the correlation constants in the vapour pressure equation.
When the vapor phase of a pure liuid is in equilibrium with its liquid phase, the equality of chemical potential, temperature, pressure in both phases leads to the Clausius-Clapeyron equation:
Most vapour pressure estimations and correlation equations stem from integration of above equation. When this is done, an assumption must be made regarding the dependence of the group (ΔHv /ΔZv ) on temperature. The simplest approach is to assume that the ΔHv /ΔZv is constant and then the above equation on integration becomes (A being the integration constant:
(where T in in K, and Δ Zv = Zvap - Zliq , Z being the compressibility factor). The above equation is called Clausius-Clapeyron equation where, B is given as ΔHv /RΔZv (ΔHv = enthalpy of vaporization). A simple modification of the equation which has been widely used is known as Antoine equation:
C = Constant, T = oC. As an approximation at low pressures (less than 1 atm), if ΔZv is taken as 1.0, the latent heat of vaporization can be directly obtained from the slope of the plot of ln P vs. 1/T .