Energy and Entropy Formulation

Both the energy formulation and the entropy formulation serve to obtain the position of equilibria. In general, it is stated that both methods are equivalent. This is basically true. However, there is a subtle difference from the point of view. 

In the energy formulation, the entropy is faced as a thermodynamic variable, formally equivalent to the other thermodynamic variables such as volume, mol numbers. The energy is treated as a function of these variables. In contrast to this view, in the entropy formulation, the entropy as such is the function, and the energy is positioned side on side with the other thermodynamic variables, such as volume, mol numbers. 

In recording, with the aid of the two quantities, energy and entropy, the relations, which translate analytically the two principles, we obtain two relations between the coefficients which occur in a given phenomenon but it may be easier and also more suggestive 

For a list of some thermodynamic functions, see Table 2.3. We will exemplify the different approaches to get the conditions of equilibrium in Sect. 6.3.6. 

We explain at first the concept of mechanical equilibrium. A common illustration is the mechanical equilibrium of two masses on an inclined plane under the action of gravity. The masses are connected with an inextensible string as shown in Fig. 6.1. 

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