By Sunil Bhardwaj

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For a two component (C = 2) system, the phase rule becomes.

F = C - P + 2 = 2 - P + 2 = 4 - P

Hence we have three degrees of freedom (F = 3) for one phase. Therefore, the three variables are necessary to describe the system. However, it is not possible to plot the three variables at a time one of the variables is always held constant therefore the number of degrees of freedom of the system is reduced by one and the modified phase rule is given by

F = C - P + 1 = 2 - P + 1 = 3 - P

This is known as condensed phase rule and the systems studied under this condition, are called condensed systems. Thus, for condensed systems, when

P = 1, F = 2 (bivariant)

P = 2, F = 1 (monovariant)

P = 3, F = 0 (non-variant) (TRIPLE POINT)