Illustrate that  for  correct  mass  balance,  relative  amounts  of  two  co-existing  phases  or microconstituents must be given by lever principle.

Ans:   Using  lever  rule one  can  conclude quantitatively  the  relative  composition  of  a mixture  in  a  two-phase  region  in  a  phase  diagram.  Distances l from the mixture point along a horizontal tie line to both phase boundaries gives the composition:

N_αl_α= N_βl_β

N_α signifies the amount of phase α and N_β represents the amount of phase β.

It can be conveniently expressed as: