Or the melting point. This is the temperature at which the liquid molecules lose the kinetic energy and cannot sustain the liquid state. And they form a crystalline structure called a solid. And a freezing or melting point is not related to vigor pressure the same way that boiling points are. By adding a solid or an impurity to a pure substance, we increase entropy and make it difficult to form a crystal structure. Therefore, more energy needs to be taken away from our system.