Phase Transition — Free Energy

The stable phase minimizes free energy F = E − T·S. Two phases cross at T* = ΔE/ΔS — the phase transition temperature.

2.00
F_solid(T) = E_solid − T·S_solid
F_gas(T) = E_gas − T·S_gas
T* = ΔE / ΔS = (E_gas − E_solid) / (S_gas − S_solid)
2.0
1.00
Transition Temperature T*
2.00
= ΔE / ΔS = 2.0 / 1.0
Solid/Liquid
—
Gas
—
Molecular animation — dots spread at T > T*
P1: T < T* → F_solid < F_gas → Solid/Liquid STABLE. Default: T*=2.0, ΔE=2, ΔS=1.
P2: T > T* → F_gas < F_solid → Gas STABLE. Exact crossover at T* = ΔE/ΔS.