ABSTRACT
The phenomenon of ‘sudden change’ of properties is the most general, and the most striking, characteristic of phase changes. In contrast with the melting transition, the solid-liquid transition frequently shows significant supercooling. In line with the nucleation and growth theory, one can interpret this as being either due to a lack of nuclei, or to the presence of a strong barrier to the growth of nuclei. Superheating at the liquid-gas transition is also relatively common. A liquid may be heated to above its normal boiling temperature, but fails to boil because of the lack of suitable nuclei. The Clausius–Clapeyron equation relates the slope of a phase boundary to the difference in entropy and volume of the phases on either side of the phase boundary. By combining the co-existence curves for liquid–gas, solid–gas and solid–vapour phases, one can construct a phase diagram for water substance.
