A relationship between the change in saturated vapour pressure and the latent heat of vaporization when there is a change of state:
(p. 69) where λ is the latent heat of vaporization, p is the saturated vapour pressure, T the absolute temperature, V the specific volume of the vapour at T, and v is the specific volume of the liquid. Assuming that the ideal gas law applies, then the equation can be written as:
The equation can also be used for the transition of a solid to a liquid. The equation is named after German physicist Rudolph Clausius (1822–88) and French engineer Benoît Paul Émile Clapeyron (1799–1864).