The behaviour of the metal during heating under a constant pressure of 1 atm can be
predicted &om the diagram :
0 At point a, the solid metal is in equilibrium with the gas phase consisting of the vapour
of M at the partial pressure of d and air (or inert gas) at the partial pressure of d-a, to
make the total pressure of 1 atm.
0 As the temperature is increased, the partial pressure (i.e., the vapour pressure) of the
metal vapour increases along the curves de and ec. Note that the metal M melts at b
during heating.
At point c, the vapour pressure of the metal M becomes identical to the ambient
pressure (latm), and hence the liquid metal boils.
0 Further heating will result in the metal being completely in the vapour phase.