PX154 - C4 - pV diagrams 2

[YF fig 18.7]

• at high temperature, very similar results from ideal gas and vdW equations
  
• vdw predictions differ at low temperatures
  • at $304K$, curve shows a point of inflexion
  • at lower temperatures, curve shows a local maximum and minimum
    • this is not physical: gas pressure doesn't change in this manner
  • to interpret this, a horizontal line is drawn such that $Are{a}_X=Are{a}_Y$
    • compressing from high volumes, it begins to liquify at $A$
    • further compression increases liquification
    • all gas is liquified at $B$
    • pressure remains constant throughout
    • note that curve is much steeper at lower volumes as liquid is difficult to compress