Standard Thermodynamic Quantities of a Chemical Reaction

The standard Helmholtz energy is defined as follows First we write the chemical potentials of A and B, in their thermodynamic representation, as 

This is the well-known relation between the chemical equilibrium K and the standard Helmholtz energy of the reaction. 

These results are quite instructive, though they were obtained for this particular simple system. The standard entropy of the reaction depends only on the ratio of the degeneracies of the two levels. The standard energy depends only on the difference in the energies of the two levels. In this example the two quantities AS° and A ° are completely independent of each other, in the sense that each depends on a different set of parameters of the molecules. In more complicated examples discussed in Chapter 8, such a neat separation of parameters does not occur. 

Two limiting cases of K are of interest. We rewrite the chemical equilibrium (2.4.45) as 

At very low temperature, the term TAS will become very small compared with AE. In this limit only the difference in the energy levels will determine the equilibrium constant. If we let r- 0, we eventually get - 0 this means that the concentration of B is zero, i.e., all molecules are in the ground state A. 

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