Exergy and Information

Information means 'acquired knowledge'. The thermody-namic concept of exergy is closely related to information. A high local concentration of a chemical compound, for instance, with a biochemical function that is rare elsewhere, carries exergy and information. On more complex levels, information may still be strongly related to exergy but in more indirect ways. Information is also a convenient measure of physical structure. A certain structure is chosen out of all possible structures and defined within certain tolerance margins.

It is possible to distinguish between the exergy of information and the exergy of biomass. pi defined as C/A, where n

is the total amount of matter in the system, is introduced as new variable in eqn [7]:

As A « Ao, exergy becomes a product of the total biomass A (multiplied by RT) and Kullback's measure:

where pi and pi are probability distributions, a posteriori and a priori to an observation of the molecular detail of the system. It means that K expresses the amount of information that is gained as a result of the observations.

If we observe a system, which consists of two connected chambers (see Figure 3), then we expect the molecules to be equally distributed in the two chambers, that is, p1 — p2 is equal to 1/2. If, on the other hand, we observe that all the molecules are in one chamber, then we get p1 — 1 and p2 — 0. Let us presume that the chamber to the left contains 1 mol of a pure ideal gas, while the

Figure 3 The left chamber contains 1 mole of a pure ideal gas, while the right chamber is empty. If we open the valve, the system will loose eco-exergy (or technological exergy) = RT ln2, which we could utilize by installation of a propeller in the valve. The entropy of the system will simultaneously increase by R ln2.

chamber to the right is empty. If we open the valve between the two chambers, the loss of eco-exergy (and also of technological exergy) for the system would be RT ln2 in accordance with eqns [7], [9], and [10]. We could utilize at least a part ofthe exergy by installation of a small propeller in the valve. The system will by this process increase its entropy R ln2. This is in accordance with eqn [8].

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