Isothermal change of state

from Wikipedia, the free encyclopedia
Comparison of the isothermal and isentropic changes in state in the pV diagram

The isothermal change of state is a thermodynamic change of state in which the temperature remains unchanged:

There denote and the temperatures before and after the change of state. When a gas is compressed, the heat of compression has to be dissipated, and when it is expanded, heat has to be added ( diabatic change of state ) . This can be achieved approximately by a heat bath .

Ideal gas

According to Boyle-Mariotte's law and the caloric equation of state of an ideal gas , the product of pressure and volume as well as the internal energy remain constant at constant temperature :


From this it follows that the pressures are inversely proportional to the corresponding volumes:

For the work done, the following applies to isothermal compression or expansion of moles of an ideal gas:


where denotes the universal gas constant .

Because is . According to the first law of thermodynamics ( ) it follows that the added or extracted heat corresponds directly to the work performed ( ).

See also

Web links

Commons : Isothermal processes  - collection of images, videos and audio files