3.D.1. Phase Diagrams

The coexistence curves of a typical pure PVT system are shown in Fig.3.4.

In general, there are 3 possible phases, namely, vapor, liquid, and solid.

All transitions are 1st order with accompanying latent heat.

Coexisting phases

Name of curve

Symmetry change

vapor-liquid

liquid-solid

vapor-solid

vaporization

fusion

sublimination

no

yes

yes

Point A is the triple point at which all 3 phases coexist.

Point C is the critical point at the end of the vaporization curve.

 

The vaporization curve AC actually denotes a vapor-liquid coexistence region as shown in the P-v diagram in Fig.3.5.  Note that the isotherms are also isobars in the coexistence region.

 

The 3-D P-v-T diagram is shown in Fig.3.6.