Explanation

Also called discontinuous transformation. The first derivative of the molar free energy function of the system with respect to some constraint variables appears discontinuous phase transformation at the phase transformation point. If only two constraint variables, temperature (T) and pressure, are considered for the unit system, the molar free energy (G) of each possible phase in the system is a surface in space, and the curve of intersection of the two surfaces gives the constraint conditions of two-phase equilibrium. At constant pressure, the first derivative of the molar free energy function with respect to temperature; At constant temperature, the first derivative of the molar free energy function with respect to pressure, when it occurs, the molar entropy of the system is discontinuous, so there is a latent heat effect when it occurs; If the molar volume is discontinuous, it will occur accompanied by a volume effect, which can be measured using an dilatometer. Often accompanied by significant thermal hysteresis.

Classification