This applet models the colligative properties. The addition of a solute to pure liquid lowers the chemical potential of the liquid, thereby increasing the boiling point, and lowering the freezing (melting) point. The effect on the melting point is more dramatic than on the boiling point.
Recall that μ, the chemical potential, for a pure substance = (∂G/∂n), so μ = -Sm.
The green line represents the chemical potential of the solid solvent, the blue line the chemical potential of the liquid, and the cyan line the chemical potential of the gas. The intersection points of the chemical potential lines are the regions of phase change, because, at equilibrium, the chemical potentials of the two phases are equal. Clicking on the "decrease μ" box will lower the chemical potential of the liquid solvent, as when a solute is added; clicking the "increase μ" box will increase the chemical potential of the liquid solvent, as if solute is removed, making the solvent more pure.
In the applet below, two "ticks" show the positions of T*f, the freezing point of the pure solvent, and T*b, the boiling point of the pure solvent, for easy reference.
© 2003-2011 by Lawrence T. Sein. All rights reserved.
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