Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: gingi85 on January 03, 2008, 06:17:03 AM
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Clapeyron's Equation States:
dP/dT = ΔtrsS/ΔtrsV
According to the text book I am reading, in order to determine the slope of the phase boundaries on the phase diagram we use
ΔtrsS = ΔtrsH/T
and substitute it in to the Clapeyron's Equation.
However, this equation for the entropy of a phase transition is only true under a constant pressure (dP=0). How then can we use it in our situation where pressure is not constant?
Am I missing something?
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i would say that the constant pressure refers to the transition. so you have the transition at various constant p's. and at every pressure this equation holds
I don't know if S=H/T even requires constant p. it requires equilibrium conditions and then p and V are constant anyway.
actually i did this with fixed volume. you change tempurates and write down the eqilibrium pressures. that way you can construct the vapor pressure curve