Maximum non-expansion work

The Helmholtz and Gibbs energies are useful also in that they define the maximum work and the maximum non-expansion work a system can do, respectively. The combination of the Clausius inequality 7dS > dq and the first law of thermodynamics dU = dq + dw gives... 

The changes of A and G in closed systems correspond to the maximum work performed by or on the system. cL4 is identical to the work carried out during an isothermal reversible change. dG is identical to the non-expansion work carried out under isothermal, isobaric, reversible conditions. In other words -dG corresponds to the maximum non-expansion work (e.g. electrical work) that can be generated by a closed system at constant p and T. 

COMMENT. As Shown by Problem 3.16, increasing the temperature does rx)t necessarily increase the maximum non-expansion work. The retetwe magnitude of ArG and is the determining tactor. 

The great importance of the Gibbs energy in chemistry is becoming apparent. At this stage, we see that it is a measure of the non-expansion work resources of chemical reactions if we know AG, then we know the maximum non-expansion work that we can obtain by harnessing the reaction in some way. In some cases, the non-expansion work is extracted as electrical energy. This is the case when electrons are transferred across cell membranes in some key reactions of photosynthesis and respiration (see Sections 5.10 and 5.11). 

Relation to maximum non-expansion work AG max,non- xp At constant temperature and pressure... 

Maximum non-expansion work w =AG Constant pressure and temperature... 

We need to consider infinitesimal changes because dealing with reversible processes is then much easier. Our aim is to derive the relation between the infinitesimal change in Gibbs energy, dG, accompanying a process and the maximum amount of non-expansion work that the process can do, diVnon-exp- We start with the infinitesimal form of eqn 2.13,... 

Another thing worth emphasizing is that in any real or non-reversible expansion, as shown in our example, the work obtained is less than the maximum obtainable (from a reversible expansion). Thus in general, rewriting (4.3),... 

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