Explain the reduced phase rule .

#### Solution

**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 .