As we have seen, both the enthalpy H as well as the entropy S are important when describing thermodynamic processes. Now the question arises, how are they interdependent, i.e., how are they connected? This interdependency is described by the Gibbs free energy G. The Gibbs free energy is often referred to as free enthalpy or free enthalpy of reaction.

The Gibbs free energy is defined as

$\begin{array}{l}G=U+pV-TS\hfill \\ =H-TS\hfill \end{array}$

(Eq. 6.59)

As stated, the enthalpy is a function of temperature and pressure which makes G likewise dependent on pressure and temperature. If all reagents are provided at STP conditions and referenced to 1 mol product, the ...

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