A thermodynamic process (a thermodynamic transformation ) is a change in the thermodynamic state ( change of state ). In the case of a state of equilibrium , this can only happen with a change in one or more external parameters ( state variable ).
In the case of quasi-static thermodynamic processes (equilibrium process), these parameters are changed so slowly that the system is in equilibrium at any point in time (or anywhere near it), i.e. it passes through a sequence of equilibrium states (→ infinitesimally small changes in state ).
Quasi-static processes are called reversible ( reversible in time) if they are reversed by reversing the change in the external parameters themselves. The system and the environment can thus be reset to their original state; the entropy does not increase.
Types of thermodynamic processes
Isobaric processes take place at constant pressure. An example can be a movable piston in a cylinder, in which the pressure inside the cylinder is always below atmospheric pressure.
An isochoric process is a process that runs at constant volume. The system does not perform any mechanical work when it is supplied with energy. If a closed system is heated, for example air in a closed can, only the internal energy of the gas is changed, that is, the temperature and pressure increase.
An isothermal process is a process that takes place at a constant temperature. Adiabatic processes are processes without heat supply or removal. Reversible adiabatic processes are identical to isentropic processes, which take place with constant entropy.
From isenthalps processes is when the enthalpy of a system does not change.
Sometimes these processes are also summarized under the term isoprocesses .
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