Question

A piston-cylinder device contains superheated steam. During an actual adiabatic process, the entropy of the steam will (never, sometimes, always) increase.

Short answer

Answer: Sometimes

Step-by-step solution

Understanding adiabatic processes

An adiabatic process is a thermodynamic process in which there is no heat transfer between the system (in this case, the steam in the piston-cylinder device) and its surroundings. In other words, the system is perfectly insulated, and any increase or decrease in the internal energy of the system comes from work done on/by the system.

Understanding entropy and its behavior

Entropy is a thermodynamic property that measures the level of disorder or randomness in a system. According to the second law of thermodynamics, the entropy of an isolated system (a system that does not exchange heat or work with its surroundings) always increases, until it reaches the maximum possible value, known as the equilibrium state. In the case of non-isolated systems, such as the steam in the piston-cylinder device, the change in entropy can be positive, negative, or zero, depending on the process.

Analyzing the adiabatic process in a piston-cylinder device

During an adiabatic process (as defined in Step 1), the piston-cylinder device is insulated from its surroundings, and no heat is exchanged between the steam and the surroundings. However, the steam and the piston-cylinder device together are not an isolated system, as work can be done on or by the steam. According to the second law of thermodynamics, the entropy change (∆S) for any real process can be calculated as follows: ∆S = ∆S_system + ∆S_surroundings Since this is an adiabatic process, ∆S_surroundings is zero because no heat is exchanged with the surroundings.

Determining if the entropy of the steam will increase

In most real (non-ideal) adiabatic processes, irreversible work is done on or by the system, which leads to an increase in entropy. In this case, since the piston-cylinder device is filled with superheated steam and undergoing an adiabatic process, the entropy of the steam will sometimes increase due to irreversible work and other real-world inefficiencies. So, the correct answer is: Entropy of the steam will "sometimes" increase during an actual adiabatic process.