Phase Diagrams

• Phase behavior is described via phase diagrams

• Gibbs phase rule

  • F = 2 + C – P
    F = number of degrees of freedom
    
    • independently specified thermodynamic state variables
    C = number of components (chemical species) in the system
    P = number of phases
  • Single component, F = 3 – P

Field variable

e.g., temperature

Density variable

L+V

tie line

V

L

S

S+V

L+S

triple point

critical point

Field variable

(pressure)

Field variable

(temperature)

V

L

S

critical point

isobar

two-phase regions

two-phase lines

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