Non Equilibrium

Solutions

In solution chemistry and biochemistry the Gibbs free energy decrease is commonly used as a surrogate for the entropy produced by spontaneous chemical reactions is situations where there is no work being done; or at least no useful work, i.e., other than perhaps some ± P dV. The assertion that all spontaneous reactions have a negative is merely a restatement of the fundamental thermodynamic relation, giving it the physical dimensions of energy and somewhat obscuring its significance in terms entropy. When there is no useful work being done, it would be less misleading to use the Legendre transforms of the entropy appropriate for constant T, or for constant T and P the  Massive functions −F/T and −G/T respectively. 

Non Equilibrium

Generally the systems treated with the  conventional chemical thermodynamics are either at equilibrium or near equilibrium. llya Prigogine developed the thermodynamic treatment of open systems that are far from equilibrium. In doing so he has discovered phenomena and structure of completely new and completely unexpected types.

The non equilibrium thermodynamics has been applied for explaining how ordered structure e.g., the biological systems, can develop from disorder.  Even if Onsager's relations are utilized, the classical principles of equilibrium in thermodynamics still show that linear systems close to equilibrium always develop into states of disorder which are stable to perturbations and cannot explain the occurrence of ordered structures.

System Constrints

In this regard, it is crucial to understand the role of walls and other constraints, and the distinction between independent processes and coupling. Contrary to the clear implication of many reference sources, the previous analysis is not restricted to homogeneous, isotropic bulk systems which can deliver only PdV work to the outside world, but applies even to the most structured  systems.  There are complex systems with many chemical "reactions" going on at the same time, some of which are really only parts of the same, over all process.  

A gas reaction which results in an  increase in the number of molecules will lead to an increase in volume at constant external pressure. If it occurs inside a cylinder closed with a piston, the equilibrated reaction can proceed only by doing work against an external force on the piston. The piston moves and conversely, if the piston is pushed inward, the reaction is driven backwards.

Similarly, a redox reaction might occur in an electrochemical cell with the passage of current in wires, connecting the electrodes. The half-cell reactions at the electrodes are constrained if no current is allowed to flow. The current might be dissipated as joule heating, or it might in turn run an electrical device like a motor doing mechanical work.  An automobile lead-acid battery can be recharged, driving the chemical reaction backwards.

The hydrolysis of ATP to ADP and phosphate can drive the force times distance work delivered by living muscles and synthesis of ATP is in turn driven by a redox chain in mitochondria and chloroplasts, which involves the transport of ions across the membranes of these cellular organelles. The coupling of processes here and in the previous examples, is often not complete. Gas can leak slowly past a piston, just as it can slowly leak out of a rubber balloon. Which determines what percentage of the driving free energy is turned into external work, or captured as "chemical work"; a misnomer for the free energy of another chemical process.