@wikipedia

where

Pure substance

For Pure substance:  $//<![CDATA[ \begin{array}{l}C=1\end{array} //]]>$ and  $//<![CDATA[ \begin{array}{l}F = 3 - P\end{array} //]]>$.

It means that 3-Phase Equilibrium (solid, liquid an gas) has zero degrees of freedom :  $//<![CDATA[ \begin{array}{l}F = 0\end{array} //]]>$ thus making a single point on Phase Equilibrium Diagram, called Triple Point and characterized by a certain  Temperature and Pressure. 

The 2-Phase Equilibrium has one degree of freedom:  $//<![CDATA[ \begin{array}{l}F=1\end{array} //]]>$ and form a smooth line on Phase Equilibrium Diagram.

Binary Mixture 

For Binary Mixture:  $//<![CDATA[ \begin{array}{l}C=2\end{array} //]]>$ and  $//<![CDATA[ \begin{array}{l}F = 4 - P\end{array} //]]>$.

It particularly means that 2-Phase Equilibrium of Binary Mixture has two degrees of freedom :  $//<![CDATA[ \begin{array}{l}F = 2\end{array} //]]>$ and covers a 2-dimensional area on Phase Equilibrium Diagram. 

See also

Natural Science / Physics / Thermodynamics / Thermodynamic system / Phase / Phase Equilibrium

[ State of matter ][ Pure substance ] [ Mixture ][ Fluid Mixture ] 

[ Thermodynamic equilibrium ][ Vapour Liquid Equilibrium (VLE) ]

[ Phase Equilibrium Diagram ]

References