6.5 The Steam Line, The Hoar Frost Line and The Ice Line

Any possibility of a spontaneous change in an isothermal isobaric process is conditioned by the corresponding negative change in the thermodynamic potential. This means that for such transformation


dG < 0

Or, by Eq. 6.21     dm (G1Gv) < 0


If G1 > Gv, then dm must be negative, that is, a quantity of liquid must evaporate. Conversely if G1 < Gv, dm must be positive, that is, a quantity of vapour must condense to the liquid state. There will evidently be no evaporation or condensation if G1 = GV This is, therefore, the condition of equilibrium between the liquid and the vapour phases. The line I in the (p − T) space over which the functional relation G1 = GV holds is called the steam ...

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