ABSTRACT
Phase transition is one of the important aspects of solid-state chemistry. Thermodynamic criteria of phase change have been discussed with reference to Gibbs free energy, Helmholtz free energy, internal energy and entropy with the help of the diagrams. Structural changes accompany phase transition. Phase rule, component and degree of freedom have been discussed with reference to one component and two component systems. Simple eutectic system such as lead–silver system has been explained with the help of phase diagram. Phase diagram of binary systems with solid solution has also been dealt with. Peritectic system of two solid solution has been shown by the phase diagram. Phase transition may be attributed to reconstructive and displacive transitions. Critical size of nuclei in nucleation and growth transition along with Avrami plot have been discussed.
