Final answer:
In thermodynamics, positive work is when a system, such as a gas in a cylinder, does work on its surroundings by expanding and exerting force on a piston. This force can be calculated as F = pA, and the work done during an isobaric process is W = PΔV, indicating positive work when the volume increase is positive.
Step-by-step explanation:
Understanding Work Done by a Thermodynamic System
When discussing the concept of work in thermodynamics, it is focused on the energy transfer that occurs when a thermodynamic system, such as a gas within a cylinder with a piston, interacts with its surroundings. This is often observed in heat engines. If we consider the gas expanding against the piston, as the gas exerts a force over a distance, it performs positive work. This is because the system (the gas) is doing work on its environment (the piston). The force that the gas exerts on the piston can be calculated using the equation F = pA, where p represents the pressure of the gas and A represents the piston area. When the piston moves outwards, the work W = pA dx, where dx is the displacement of the piston. In an isobaric process, where the pressure remains constant, the work done is given by the equation W = PΔV, which indicates that if the volume change (ΔV) is positive, the work done by the gas on the piston is also positive.
In the context of a heat engine, when fuel combustion occurs, heat transfer to the gas causes it to expand, exerting a force and moving the piston to perform work. This process is fundamental to how engines operate, translating thermal energy into mechanical work. These processes are also subject to the first law of thermodynamics, which involves the internal energy of the system, heat added to the system, and work done by the system.