Question

Explain the reduced phase rule .

Answer 1

i)  In two component system , when P=2 and C=2
               F=C-P+2=3.
ii) Since the maximum number of degrees of freedom in a two-component system is three , the phase behaviour of a binary system may be represented by a three dimensional diagram of pressure , temperature and composition or space models , which cannot be conveniently shown on paper .
iii) A solid-liquid equilibrium of an alloy has practically no gas phase and the effect of pressure is small on this type of equilibrium ,since the experiments are conducted under atmospheric pressure.
iv) Keeping the pressure constant of a system , in which vapour phase is not considered , is known as Condensed System.
v)  It will reduce the degree of freedom by one and for such a system , phase rule becomes
             F=C-P+1
This is known as the reduced/condensed phase rule having two variables ,namely temperature and concentration of constituents .