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**Unformatted text preview: **Clausius-Clapeyron equation is applicable to solid-vapor equilibrium as well.
The pressure plotted in the phase diagrams and used in these relationships is the
vapor pressure of the substance under consideration, not the total pressure. Eq.
(5.14) gives the P-T relationship required to plot the lines in the phase diagrams.
Therefore, Eq. (5.14) for the liquid-vapor and the solid-vapor equilibria can be
used to find the triple point for a one-component system.
Examples 5.2, 5.3, Problems 5.1–5.4, 5.7–5.10, 5.12, 5.15, 5.18, 5.20.
2 The Gibbs Equation:
By definition,
dG = VdP – SdT.
At constant temperature, the second term vanishes and we get
dG = VdP.
For the liquid vapor equilibrium considered earlier, under these circumstances, we
have
dGm,v = dGm,l
or
Vm,vdP = Vm,ldPt,
where the pressure term on the vapor side is the vapor pressure of the substance
while on the liquid side, it is the total pressure acting on the liquid surface. Now,
using ideal gas law for the vapor, we get
RT dP = V dP or
m,l
t
P
dP = V m,l dP .
P
RT t
Now consider a situation...

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