Non-expansion work

If the heat is transferred at constant volume and no non-expansion work is done,... 

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 total amount of work is conveniently separated into expansion (or pV) work and non-expansion work. 

For a reversible change in a closed system and in the absence of any non-expansion work this equation transforms into... 

Thus in the absence of non-expansion work for a closed system, the following important equation... 

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. 

Enthalpy change at constant pressure, no non-expansion work... 

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,... 

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). 

At pH = 7.0 and 37°C (310 K, blood temperature) the enthalpy and Gibbs energy of hydrolysis are A H = —20 kj moT and Afi = —31 kj moT , respectively. Under these conditions, the hydrolysis of 1 mol ATP (aq) results in the extraction of up to 31 k) of energy that can be used to do non-expansion work, such as the synthesis of proteins from amino acids, muscular contraction, and the activation of neuronal circuits in our brains, as we shall see in Chapter 5. If no attempt is made to extract any energy as work, then 20 kJ (in general, AH) of heat will be produced. 

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... 

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