Nonexpansion work

A system can do two kinds of work. The first type is expansion work, the work needed to change the volume of a system. A gas expanding in a cylinder fitted with a piston pushes out against the atmosphere and thus does expansion work. The second type of work is nonexpansion work, work that does not involve a change in volume. A chemical reaction can do nonexpansion work by causing an electrical... 

In a constant-volume system in which neither expansion work nor nonexpansion work is done, we can set w = 0 in Eq. 7 (At/ = tv + q) and obtain... 

The challenge that we now face is to justify these remarks and to derive a quantitative relation between the Gibbs free energy and the maximum nonexpansion work that a system can do. 

At this point, we recognize that the system may do both expansion work and nonexpansion work ... 

This important relation tells us that, if we know the change in Gibbs free energy of a process taking place at constant temperature and pressure, then we immediately know how much nonexpansion work it can do. For instance, for the oxidation of glucose,... 

The change in Gibbs free energy for a process is equal to the maximum nonexpansion work that the system can do at constant temperature and pressure. 

J 13 Estimate the maximum nonexpansion work that can he done by a process (Section 7.14). 

What Do We Need to Know Already This chapter extends the thermodynamic discussion presented in Chapter 7. In particular, it builds on the concept of Gibbs free energy (Section 7.12), its relation to maximum nonexpansion work (Section 7.14), and the dependence of the reaction Gibbs free energy on the reaction quotient (Section 9.3). For a review of redox reactions, see Section K. To prepare for the quantitative treatment of electrolysis, review stoichiometry in Section L. 

To find the connection between cell potential and Gibbs free energy, recall that ir Section 7.14 (Eq. 21) we saw that the change in Gibbs free energy is the maximum nonexpansion work that a reaction can do at constant pressure and temperature ... 

A fundamental equation combines the first and second laws of thermodynamics and, in this manner, addresses the behavior of matter. For a reversible change in a closed system of constant composition and without nonexpansion work, one can write... 

At this point, we recognize that the system may do both expansion work and nonexpansion work. Reversible expansion work (achieved by matching the external pressure to the internal) is given by d revexpansion = —PdV (Eq. 9 of Chapter 6), so... 

From tables of standard free energies of formation, we find AG,° = -2885 kj-mol-1. Therefore, the maximum nonexpansion work obtainable from 1.00 mol C6H1206(s) is 2.88 X 103 kj. About 17 kj of work must be done to build 1 mol of peptide links (a link between amino acids) in a protein, so the oxidation of 1 mol (180 g) of glucose can be used to build up to about 170 mol of such links. More visually the oxidation of one glucose molecule is needed to build about 170 peptide links. In practice, biosynthesis occurs indirectly, there are energy losses, and only about 10 such links can be built. A typical protein has several hundred peptide links, so several dozen glucose molecules must be sacrificed to build one protein molecule. 

Helmholtz energy (sometimes also called Helmholtz free energy, or Helmholtz function) is the thermodynamic state function equal to the maximum possible nonexpansion work output, which can be done by a closed system in an isothermal isochoric process (T = const, V = const). In terms of the -> internal energy and -> entropy... 

This nonexpansion work can be extracted from the system as electrical work, as in the case of a chemical reaction taking place in an electrochemical cell, or the energy can be stored in biological molecules such as adenosine triphosphate (ATP). 

---