The change in free energy during solidification is made
up of two terms - the change in enthalpy during fusion,
DHf (i.e.
the latent heat ) and the change in energy associated with
the entropy change during fusion, DSf.
DGf
= DHf -TDSf
Click
on the labels on the image on the right to show free energy,
DHf and -TDSf
curves.
DSf represents
the increase in the degree of disorder on going from the
regular atomic array of the (crystalline) solid to the disorganized
atomic structure of the liquid. Using the condition that
DGf=0 when
T=Tf leads to an expression
for the entropy of fusion in terms of the latent heat DSf
=DHf /Tf
so that the free energy change can be written as DGf
= DSfDT.
On the image, click the temperature where DHf
= TDSf.
