Interpretation of Free Energy

You have seen that the free-energy change serves as a criterion for spontaneity of a chemical reaction. This gives you some idea of what free energy is and how you interpret it. In this section, we will look more closely at the meaning of free energy. 

Theoretically, spontaneous reactions can be used to obtain useful work. By useful work, we mean energy that can be used directly to move objects of normal size. We use the combustion of gasoline to move an automobile, and we use a reaction in a battery to generate electricity to drive a motor. Similarly, biochemical reactions in muscle tissue occur in such a way as to contract muscle fibers and lift a weight. 

Shown are ionic forms of adenosine triphosphate (ATP) and adenosine diphosphate (ADP). The rings have carbon atoms at the junctures. 

The mitochondria are parts of a cell that obtain energy in the form of ATP from glucose (from food), C6Hi20g. ATP molecules are used in various cell processes, such as protein synthesis from amino acids, which occurs in the ribosomes. 

The sign of w (work) is defined so that a negative value means work obtained from the system (that is, energy is subtracted from the system). You can obtain work from a reaction if its AG is negative. 

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Interpretation of free Energy Free Energy and Equilibrium Constants... 

To sununarize, although the total free energy of a system is a state function, free energy components are not. Free energy components are essentially a reflection of the path (or the reference ensemble) that has been imposed and any analysis or physical interpretation of free energy components based on such calculations is subjective. 

Calculation of the standard free energy of binding itself can be viewed as a special case of the above, in which one of the pair of ligands contains no atoms.10 Some care is required to be sure that such calculations yield answers that actually correspond to the desired standard state.11 12 Unfortunately, many calculations of free energies of binding have not made appropriate contact with a standard state, so that results in the literature must be interpreted with caution. 

The derived formula (19) shows the dependence of free energy f2 of the PtHx phase on temperature T, concentrations ci, c2, c of < i, 2 fullerenes and hydrogen, degree of ordering r 2 in this phase and energetic constants of pair interaction between 4>n- 4>m(n,m=l,2) fullerenes, fullerenes and platinum atoms, fullerenes and hydrogen atoms. Below we shall study the free energy f2 for hydrofulleride for the purpose of interpretation of calculation results. 

There are many techniques of varying degrees of generality for the study of mechanisms and that of free energy relationships is the most readily applicable and general. Free energy relationships comprise the simplest and easiest of techniques to use but the results are probably the trickiest to interpret of all the mechanistic tools. 

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