I was just going through a graph of isotherm given by cubic equation of state and noticed that isotherms passes trough the subcooled liquid region. Are these equation applicable to liquids?
Cubic equations of state are summarized here. They can, indeed, describe both the liquid and gaseous state.
Under subcritical conditions, a given temperature and pressure will give three roots. The largest is the vapor volume, the smallest is the liquid volume and the middle one is an unstable state that must exist along with the vapor and liquid roots. By using appropriate integrated forms we can compare the free energies associated with these roots and thus identify which is more stable. Or, we can identify when the free energies match and thus predict vapor-liquid equilibrium. The catch? The equations are of only limited accuracy, especially for liquids. Some are better than others; for more details the reader can start with the Wikipedia reference given above (https://en.m.wikipedia.org/wiki/Equation_of_state).