Phase Diagrams

Implicit in the discussion above is the fact that the phase in which a substance finds itself is a
function of external conditions. On a plot of pressure versus temperature, one can imagine dividing
the area of the quadrant into three sections, one corresponding to each of the three phases. The x
and y values falling within each section are all the combinations of the pressure and temperature
values at which the substance will be in that phase. In general, the gas phase is found at high
temperature and low pressure; the solid phase is found at low temperature and high pressure; and
the liquid phase is found at high temperature and high pressure. A typical phase diagram is shown
below:

BASIC CONCEPT

In  a   phase   diagram,    the point   at  which   all three   lines   intersect   is  called  the triple  point.

The three phases are demarcated by lines indicating the temperatures and pressures at which two
phases are in equilibrium. Along line A, the solid and liquid phases are in equilibrium; along line B,

Triple  Point