A simple example of second-order phase transitions is the liquid-vapor transition at the critical point. In this case, the liquid transforms continuously into a vapor without a discontinuous change in the volume. At the critical point, the two phases are indistinguishable and there is no latent heat in this transition. However, the critical points are not very common in solid state physics due to symmetry restrictions.

The second order phase transition, different from the first order phase transition, is continuous across the transition temperature or other transition parameter. The thermodynamic parameters are continuous, but their first derivatives are discontinuous.