Intensive and extensive properties

An extensive quantity is a state variable that varies with the size of the system under consideration. Examples are mass, amount of substance, volume, entropy and the thermodynamic potentials (internal energy, free energy, enthalpy and Gibbs free energy ). The counterpart of the extensive quantity is the intensive quantity.

The function of a size of the system considered, for example, be tracked on the basis of two identical systems, which are separated by an intermediate wall. If you raise this separation on and extends the observation to the entire system, so the difference between intensive and extensive quantities is clear: all sizes now have the same value as before the removal of the partition, are intensive quantities; However, all sizes now have a different value, extensive quantities.

It is possible to convert extensive quantities in intensive quantities, by being related to a certain mass (specific size) or to a certain amount of substance ( molar size). The volume of the molar volume, however, it is an extensive quantity, an intensive quantity.

The change of an extensive quantity must be followed by no change in the thermodynamic equilibrium.

• Thermodynamic state variable