The lever rule for a binary system with vapor and liquid in equilibrium:

\[aL = bV\]

where \(a\) and \(b\) are the distances in the figure above and \(L\) and \(V\) are the number of moles of liquid and vapor, respectively.

The lever rule can also be written as:

\[(z_h – x_h)L = (y_h -z_h)V\]

where\(x_h\) and \(y_h\) are the liquid and vapor fractions, respectively, and \(z_h\) is the overall mole fraction of the mixture.