12. Derivation of Phase rule:
To be more specific, the composition of each phase is determined
by C − 1 intensive variables (such as mole fractions) in each phase. The total
number of variables is (C − 1)P + 2, where the extra two are temperature and
pressure. The number of equations is C(P − 1), since the chemical potential of
each component must be equal in all phases.
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14. Thus each area of phase diagram represents a
bivariant system. At conditions wholly within
one of the three areas, both the variables
(pressure and temperature) can be varied
independently without causing a change in the
state of equilibrium. Therefore in order to define
the condition of the phase both pressure and
temperature must be stated.
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