# Change of state

A change of state is generally used to describe the change in a system from one state to another.

## Change of state in the field of biology

In biology , such changes of state can be found in metamorphosis or dying .

## Change of state in the field of physics

The physics is concerned essentially with the description and the change of conditions.

### Term in mechanics

The physical quantity of acceleration describes the change in the state of motion of a body.

### Term in thermodynamics

In thermodynamics , on the one hand, the changes in aggregate states and the associated phase transitions of substances should be mentioned, which are always associated with a change in entropy . Examples of this are the melting of ice or the evaporation and condensation of water.

On the other hand, changes in the state of gases are described. The thermodynamic system is transferred from one state to another. A simple change of state is e.g. B. observed in a balloon that was filled with a gas on a summer day at high temperature. If this comes into an air-conditioned room, the balloon shrinks. A distinction is made between the following special cases of state changes:

a)  Isobaric change of state (constant pressure)
b)  Isochore change of state (constant volume)
c)  Isothermal change of state (constant temperature)
d)  Adiabatic change of state (no exchange of thermal energy )
e)  Isentropic change of state (no change in entropy of the overall system)
f)  Isenthalpic change of state (no change in the enthalpy of the overall system)
g)  Polytropic change of state

The state changes a) to f) are special cases of g). In the case of the change of state g) (polytropic change of state), the exponent can theoretically assume any value between and + . It should be noted that these changes of state are idealizations , because with real changes of state n is not constant either. ${\ displaystyle - \ infty}$${\ displaystyle \ infty}$

### Term used in atomic, nuclear and quantum physics

In the microphysical specialty areas of atomic , nuclear and quantum physics , the change in energy states is described above all .