Intensive Properties

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An intensive property is a physical quantity whose value does not depend on the amount of the substance for which it is measured. For example, the temperature of a system in thermal equilibrium is the same as the temperature of any part of it. If the system is divided the temperature of each subsystem is identical. The same applies to the density of a homogeneous system: if the system is divided in half, the mass and the volume change in the identical ratio and the density remains unchanged.

According to the state postulate, for a sufficiently simple system, only two independent intensive variables are needed to fully specify the entire state of a system. Other intensive properties can be derived from the two known values.

Some intensive properties, such as viscosity, are empirical macroscopic quantities and are not relevant to extremely small systems. Combined intensive properties

There are four properties in any thermodynamic system, two intensive ones and two extensive ones.

If a set of parameters, \{a_i\}, are intensive properties and another set, \{A_j\}, are extensive properties, then the function F(\{a_i\},\{A_j\}) is an intensive property if for all \alpha,

F(\{a_i\},\{\alpha A_j\}) = F(\{a_i\},\{A_j\}).\,

It follows, for example, that the ratio of two extensive properties is an intensive property - density (intensive) is equal to mass (extensive) divided by volume (extensive). Joining systems
This section's factual accuracy is disputed. (February 2009)

Let there be a system or piece of substance a of amount ma and another piece of substance b of amount mb which can be combined without interaction. [For example, lead and tin combine without interaction, but common salt dissolves in water and the properties of the resulting solution are not a simple combination of the properties of its constituents.] Let V be an intensive variable. The value of variable V corresponding to the first substance is Va, and the value of V...
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