The concept of thermodynamic work

Appendix G gives a detailed analysis of energy and work based on the behavior of a collection of interacting particles moving according to the principles of classical mechanics. The analysis shows how we should evaluate mechanical thermodynamic work. Suppose the displacement responsible for the work comes from linear motion of a portion of the boundary in the -Fx or —x direction of the local frame. The differential and integrated forms of the work are then given by  

1 strictly speaking, it is the sum of the energies of the system, the surroundings, and any potential energy shared hy both that is constant. The shared potential energy is usually negligible or essentially constant (Sec. G.5). Some thermodynamicists treat radiation as a separate contribution to AU, in addition to q and w. 

Thermodynamics and Chemistry, second edition, version 3 2011 by Howard De foe. Latest version Hww.chem.vimd.edu/thermobook 

The kind of force represented by is a short-range contact force. Appendix G shows that the force exerted by a conservative time-independent external held, such as a gravitational force, should not be included as part of This is because the work done by this kind of force causes changes of potenhal and kinetic energies that are equal and opposite in sign, with no net effect on the internal energy (see Sec. 3.6). 

Newton s third law of action and reaction says that a force exerted by the surroundings on the system is opposed by a force of equal magnitude exerted in the opposite direcrion by the system on the surroundings. Thus the expressions in Eq. 3.1.1 can be replaced by 

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