Chem 205 lecture 10
• Slopes of phase diagrams(P vs T) are usually positive
• The slope is: dP/dT and can also be seen as ∆S/∆V for a phase change slope
o Hypothetical situation: liquidgas. ∆S>0, ∆V>0, thus the slope is positive. This
applies for most other phase changes. If we take the opposite situation, in which
a gas becomes a liquid, ∆S<0, ∆V<0—the negative signs on top and bottom
cancel out, to yield the positive slope!
o At any point on a curve of the phase diagram, 2 states are in equilibrium (aka, 2
• The vapor pressure at equilibrium ONLY depends on Temperature (only 1 df)
o At triple point, no DF, P, V, T are all predetermined.
• The critical poi