A phase transition may be defined as some smooth, small change in a quantitative input variable that results in an abrupt qualitative change in the system’s overall state. The transition of ice to steam is one example of a phase transition. At some critical temperature, a small change in the system’s input temperature value results in a systemic change in the substance after which it is governed by a new set of parameters and properties, for example, we can talk about cracking ice but not water, or we can talk about the viscosity of a liquid but not a gas as these are in different phases under different physical regimes and thus we describe them with respect to different parameters.