Which of the following describes an adiabatic process?

An adiabatic process is defined as one in which no heat is transferred into or out of the system. This occurs when a system is perfectly insulated from its surroundings, meaning that all changes in internal energy are due to work done on or by the system rather than heat exchange. This is a fundamental concept in thermodynamics, particularly relevant in the study of gases and engines, where adiabatic processes help to explain how gases expand or compress without heat exchange.

In an adiabatic process, any change in the system's temperature is a result of work done on or by the system, not from heat transfer. This can lead to temperature changes when gas expands or is compressed, demonstrating the principles of energy conservation.

Other options describe processes that do not align with the definition of adiabatic processes. Constant temperature refers to isothermal processes, work can be done during adiabatic processes, and irreversibility does not define an adiabatic process specifically—adiabatic processes can be reversible or irreversible. Thus, the definition of an adiabatic process most accurately corresponds to the lack of heat or mass transfer.