I was trying to understand that in the plateau region of the PCT curve, we use the Van't hoff Equation, even if we considered the sloping factor we will have the following equation:

ln(P/Po)=ΔH*R*T+−ΔS*R+fs(C−Cm)

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This equation was considered in the following research paper:

link:https://doi.org/10.1016/0360-3199(94)90097-3

here for the sake of mathematical calculations, if we consider that the sloping factor is zero, the equation transforms to:

ln(P/Po)=ΔH*R*T+−ΔS*R

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By logic, why does the concentration increase during the plateau region even at constant pressure and temperature? Can anyone explain what will cause the change in the concentration in the PCT curve when considering the Van't Hoff Equation at continuous pressure and temperature, assuming we are going with an ideal PCT curve with a straight horizontal line in the PCT curve?