adiabat

An adiabat is a curve on a thermodynamic diagram representing a process in which no heat is transferred into or out of the system. This is known as an adiabatic process. During an adiabatic process, the internal energy of a system changes solely due to work done on or by the system. For an ideal gas, an adiabatic process can be described by the relation PV^gamma = constant, where P is pressure, V is volume, and gamma is the adiabatic index (the ratio of specific heats). The adiabatic index is a property of the gas, typically greater than 1. In contrast, an isotherm represents a process occurring at constant temperature, where heat transfer is allowed to maintain the temperature. Adiabatic processes are important in understanding phenomena such as the expansion of gases in engines, the formation of clouds, and the behavior of stars. Unlike isothermal expansion which cools a gas, adiabatic expansion causes a decrease in temperature because the gas does work on its surroundings at the expense of its internal energy. Conversely, adiabatic compression leads to an increase in temperature. The concept of an adiabat is fundamental in thermodynamics and is often visualized on pressure-volume diagrams.