Limitations of phase rule:

• Phase rule can be applied for systems in equilibrium only.
• It is not of much help in case of systems which attain the equilibrium state very slowly.
• It applies only to a single equilibrium state. It does not indicate the other possible equilibria in the system.
• Phase rule considers only the number of phases but not their quantities. Even a minute quantity of the phase, when present, accounts towards the number of phases.
• Hence, care has to be taken in deciding the number of phases existing in the equilibrium state.
• All the phases of the system must be present under the same conditions of temperature, pressure and gravitational forces.
• The solid, liquid phases should not be so finely sub-divided as to bring about deviation from their normal values of vapour pressure.