
304 The Principles of Thermodynamics
it is easy to see that entropy at all temperatures, according to Debye theory, is given
by
S(T)=3R{4
T
3
Θ
3
Θ
T
0
dx
x
3
e
x
−1
−ln(1 −e
−
Θ
T
)} (15.22)
It is straightforward to work out the high temperature behaviour of the Debye entropy
now:
S(T ) → 3R ln T +4R − 3R ln Θ (15.23)
This explicit example clearly demonstrates how the Nernst-Planck theorem, namely
the requirement of vanishing entropy at absolute zero, fixes the entropy constant.
In figure 15.1, a comparison is made between the specific heat of solid silver as
predicted by the Debye theory and experimental data for silver. Clearly, the agree-
ment is very good.
Now we carry ...