
176 The Principles of Thermodynamics
T
e
=37.9646
◦
C = 311.1146K. The entropy lost by water is 90 ·4Rln(T
e
/313.15)
while that gained by alcohol is 46 ·2Rln(T
e
/303.15. The net gain in entropy
during thermalization is therefore 0.0383 R=0.318 J/K.
The entropy of mixing is on the other hand −5Rln(5/6) − Rln(1/6) =
2.703R =22.475J/K. Thus we see that entropy increase due to mixing far
exceeds the entropy gain due to thermalization. Both are positive, pointing to
the irreversibility of both processes.
Example 9.2: Mixing entropy for polymers in Flory-Huggins(FH) theory
This example is to show how the ideal mixing entropy, first shown for ideal gases and
then