Intense size
An intensive variable is a state variable that does not change with different sizes of the system under consideration . A distinction is native intensive variables such as temperature and pressure , and material's intensive variables, like all molar and specific quantities of pure substances .
The counterpart to the intensive quantities are the extensive quantities , such as particle number , volume , energy and entropy , which change with the size of the system (scaling).
The dependency of a variable on the system under consideration can be traced, for example, using two identical systems that are separated by a partition. If one removes this separation and extends the consideration to the entire system, the difference between intensive and extensive quantities becomes clear: All quantities which now have the same value as before the removal of the partition are intensive quantities; on the other hand, all quantities which now have a different value are extensive quantities.
It is possible to convert extensive quantities into intensive quantities by relating them to a certain mass ( specific size ), to a certain volume (density of size) or to a certain amount of substance ( molar size ). The volume is an extensive quantity, but the molar volume is an intensive quantity.
The change in an intense quantity results in a change in the thermodynamic equilibrium .
| extensive | intensive | |
|---|---|---|
| Characteristic | Sizes depend on the amount of fabric | Sizes do not depend on the amount of fabric |
| property | Changes with the size of the system under consideration. Extensive sizes are additive. If the amount of substance is multiplied, all extensive quantities multiply. | Is not affected by the size of the system. Intense sizes are not additive. |
| Examples | Amount of substance n , volume V , internal energy U , free energy F , free enthalpy G , mass m , electrical charge Q | Temperature T , density ρ , pressure p , concentration c = n / V , viscosity , refractive index , electrical voltage U , permittivity ε , dipole moment |
| Specialty | A state variable is also extensive if it is proportional to all other state variables known to be extensive. The proportionality only applies as long as all non-extensive state variables remain constant. | The ratio of extensive quantities is an intensive quantity. |
| context | The product of an extensive and an intensive quantity is an extensive quantity | |
Web links
- intense sizes. In: Spectrum Lexicon of Physics.
Individual evidence
- ↑ Karl Schwister , Volker Leven: process technology for engineers: A teaching and practice book . Carl Hanser Verlag GmbH Co KG, 2014, ISBN 3-446-44001-1 , p. 17 ( limited preview in Google Book search).