What is true about an adiabatic process?

In an adiabatic process, the defining characteristic is that no heat flows into or out of the system. This is due to the system being perfectly insulated, meaning that any energy transfer that occurs is strictly through work done on or by the system. Because there is no exchange of thermal energy with the surroundings, any changes in the internal energy of the system are solely a result of work interactions.

In adiabatic processes, the temperature of the system can change as work is done, which distinguishes it from isothermal processes where temperature remains constant. Thus, temperature and pressure can vary depending on the work done, making the notion of constant temperature and pressure not applicable.

Additionally, while energy conservation is a principle that governs all physical processes, it is specifically more nuanced in an adiabatic context as the mechanical work affects the internal energy directly without the intervention of heat transfer. Thus, while total energy remains conserved, it does not capture the unique features of an adiabatic process itself, which is more concerned with the absence of heat transfer. Therefore, the statement that summarizes the essential nature of an adiabatic process accurately is that no heat flows in or out of the system.