## Chapter 6

## The Third Law of Thermodynamics

#### 6.a. The Nernst Heat Theorem

The first and second laws of thermodynamics have enabled us to tabulate enthalpies (sec. 3.a) and free energies (sec. 5.f) of substances. A similar tabulation of value of S^{0} is desirable. Entropy changes can be calculated (sec. 4.e.2). The entropy of one mol of any substance at a temperature T, and at a given pressure can be expressed as

(sec. 4.e.2). Here S_{0} is the hypothetical entropy at absolute zero. If S_{0} is known, one can calculate the entropy of a substance at any temperature from heat capacity data. This chapter describes such attempts.

By using the Gibbs–Helmholtz ...