Thermodynamic Process - Overview

Overview

A thermodynamic process can be visualized by graphically plotting the changes to the system's state variables. In the example, four processes are shown. Each process has a well-defined start and end point in the pressure-volume state space. In this particular example, processes 1 and 3 are isothermal, whereas processes 2 and 4 are isochoric. The PV diagram is a particularly useful visualization of a process, because the area under the curve of a process is the amount of work done by the system during that process. Thus work is considered to be a process variable, as its exact value depends on the particular path taken between the start and end points of the process. Similarly, heat may be transferred during a process, and it too is a process variable. In contrast, pressure and volume (as well as numerous other properties) are considered state variables because their values depend only on the position of the start and end points, not the particular path between them.