1. Statements of the third law
The third law of thermodynamics is concerned with the behavior of systems in equilibrium as temperature approaches absolute zero.
As long as we deal in differences in entropy, knowledge of S0 is unnecessary.
However, absolute entropy IS important, e.g.
F = U - TS
G = H - TS

2. Statements of the third law
The Gibbs-Helmholtz equation:
For an isothermal process:
These equations imply:

3. Statements of the third law
Nernst postulated the following:

4. Statements of the third law
Nernst postulate implies that:

5. Statements of the third law
The Nernst formulation of the Third Law:
‘All reactions in a liquid or solid in thermal equilibrium take place with no change of entropy in the neighborhood of absolute zero.’

6. Statements of the third law
Planck later postulated that:

7. Statements of the third law
Planck’s statement of the Third Law:
‘The entropy of a true equilibrium state of a system at absolute zero is zero.’

8. Statements of the third law
Another statement of the Third Law is:
‘It is impossible to reduce the temperature of a system to absolute zero using a finite number of processes.’

9. Step 1: Isothermal increase of H
H2 > H1 T T3 T2 T1

10. Step 2: Adiabatic demagnetization
B2 > B1 T T3 T2 T1