Statements of the third law

1. Statements of the third law • 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 • The third law of thermodynamics is concerned with the behavior of systems in equilibrium as temperature approaches absolute zero.

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

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 H M S H1 H2 > H1 T T1 T3 T2

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