The basis for the rule ( Atkins and de Paula, justification 6.1 ) is that equilibrium between phases places a constraint on the intensive variables.
12.
If two systems, and, have identical intensive variables, a thermodynamic operation of wall removal can compose them into a single system,, with the same intensive variables.
13.
If two systems, and, have identical intensive variables, a thermodynamic operation of wall removal can compose them into a single system,, with the same intensive variables.
14.
When two systems are in contact equilibrium with respect to a particular kind of permeability, they have common values of the intensive variable that belongs to that particular kind of permeability.
15.
Considering equilibrium states, M . Bailyn writes : " Each intensive variable has its own type of equilibrium . " He then defines thermal equilibrium, mechanical equilibrium, and material equilibrium.
16.
It is likewise possible to shift the dependence of the energy from the extensive variable of entropy,, to the ( often more convenient ) intensive variable, resulting in the free energies.
17.
When boundaries impose to the system different local conditions, ( e . g . temperature differences ), there are intensive variables representing the average value and others representing gradients or higher moments.
18.
Thus, when local thermodynamic equilibrium prevails in a body, temperature can be regarded as a spatially varying local property in that body, and this is because temperature is an intensive variable.
19.
For example, in thermodynamics, according to the state postulate, a sufficiently simple system consisting of a single substance requires only two independent intensive variables to fully specify the system's entire state.
20.
Accordingly, he writes : " If all the intensive variables become uniform, " thermodynamic equilibrium " is said to exist . " He is not here considering the presence of an external force field.
