Thermodynamics

cen84959_ch03.qxd 4/1/05 12:31 PM Page 122SOLIDSOLIDSOLID + LIQUIDSOLID + LIQUIDLIQUIDLIQUID122 | ThermodynamicsPCriticalpointVAPORLIQUID + VAPORFIGURE 3–21P-v diagram of a substance thatcontracts on freezing.Triple lineSOLID + VAPORvPCriticalpointVAPORLIQUID + VAPORTriple lineFIGURE 3–22P-v diagram of a substance thatexpands on freezing (such as water).SOLID + VAPORvthe solid–liquid saturation region. The T-v diagrams look very much like theP-v diagrams, especially for substances that contract on freezing.The fact that water expands upon freezing has vital consequences innature. If water contracted on freezing as most other substances do, the iceformed would be heavier than the liquid water, and it would settle to thebottom of rivers, lakes, and oceans instead of floating at the top. The sun’s