# Isentropic change of state

In thermodynamics , a process or a flow is called **isentropic** if the entropy does not change:

As **Isentropic** lines are called the same entropy . Since entropy and potential temperature are directly related to each other, the term isentropic is also used synonymously for lines of equal potential temperature.

An adiabatically reversible process is always isentropic, but this does not apply to the reverse.

The isentropic change of state of ideal gases can be described by Poisson's equations:

there are:

- v = specific volume
- p = pressure
- T = absolute temperature
- = Isentropic exponent .

The index 0 indicates the initial state, the variables without an index are the variables .