Work

Work is one of the basic modes of energy transfer. The work done by a system is a path function, and not a point function. Therefore, work is not a property of the system, and it cannot be said that the work is possessed by the system. It is an interaction across the boundary. What is stored in the system is energy, but not work. A decrease in energy of the system appears as work done. Therefore, work is energy in transit and it can be indentified only when the system undergoes a process.

Work must be regarded only as a type of energy in transition across a well defined, zero thickness, boundary of a system. Consequently work, is never a property or any quantity contained within a system. Work is energy driven across by differences in the driving forces on either side of it. Various kinds of work are identified by the kind of driving force involved and the characteristic extensive property change which accompanied it. Work is measured quantitatively in the following way. Any driving force other than temperature, located outside the system on its external boundary, is multiplied by a transported extensive property change within the system which was transferred across the system boundary in response to this force. The result is the numerical value of the work associated with this system and driving force. In static Equilibrium, F=PA (Fig 4.1). The dX is small so that P does not change. The change in volume of the gas = AdX. The elemental work,

Figure 4.1