The concepts of Hesss law can be expanded to include changes in entropy and in Gibbs free energy, since these are also state functions. The Bordwell thermodynamic cycle is an example of such an extension that takes advantage of easily measured equilibria and redox potentials to determine experimentally inaccessible Gibbs free energy values. Combining ΔG</sup> values found with Hesss law can be helpful in determining entropy values that have not been measured directly and therefore need to be calculated through alternative paths.
For the free energy:
For entropy, the situation is a little different. Because entropy can be measured as an absolute value, not relative to those of the elements in their reference states (as with ΔH</sup>), there is no need to use the entropy of formation; one simply uses the absolute entropies for products and reactants: