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Extensive variable)
In physics and chemistry, an extensive quantity (also referred to as an extensive variable) is a physical quantity whose value is proportional to the size of the system it describes. In general, this means that such a property can be expressed as the sum of the values assumed in each of the subsystems that compose the total system.
From a mathematical point of view, F is an extensive quantity if, for all α,
where V is volume and N is number of particles. Thus, extensive quantities are homogeneous functions (of degree 1) of volume and particle number.
Extensive quantities should be contrasted with intensive quantities, which are intrinsic to the system and remain constant regardless of the size of the system. Dividing one extensive quantity by another will give an intensive quantity.
Examples
Some examples of extensive thermodynamic quantities are
