Question

Draw the phase diagram of one component system and find out the number of degree of freedom along the curves and areas .

Answer 1

1)Curve OA ( Vapour Pressure curve )
Along this curve , the two phases water and water vapour coexist in equillibrium .

Water system is one component system .
Hence there are two phases ,P=2 and one component ,C=1
        F = C-P+2 =1-2+2 =1
The system is univariant .
2)Curve OB ( Sublimation curve )

Along this curve , the two phases solid-ice and water-vapour coexist in equillibrium .
Hence , P = 2 and C =1
         F = C-P+2 =1-2+2 =1
The system is univariant .
3)Curve OC ( Fusion curve )
Along this curve ,the two phases solid-ice and water coexist in equillibrium . Hence , P =2 and C =1
        F = C-P+2 =1-2+2 =1
The system is univariant .

4) Areas AOC , AOB and BOC
These areas between the curves show the conditions of temperature and pressure under which a single phase exists.
Area AOC represents conditions for liquid water ,i.e. water .
Area AOB represents conditions for gaseous phase ,i.e. water vapour . 

Area BOC represents conditions for solid phase ,i.e. ice .
In all th three areas ,thereis one phase and one component ,
           F = C-P+2 = 1-1+2 = 2
Hence , the system along the areas is bivariant .