A thermodynamic operation requires a contribution from an independent external agency, that does not come from the passive properties of the systems.
A Maxwell's demon conducts an extremely idealized and naturally unrealizable kind of thermodynamic operation.
[5] Another commonly used term that indicates a thermodynamic operation is 'change of constraint', for example referring to the removal of a wall between two otherwise isolated compartments.
[6] A typical thermodynamic operation is externally imposed change of position of a piston, so as to alter the volume of the system of interest.
A typical thermodynamic process consists of a redistribution that spreads a conserved quantity between a system and its surroundings across a previously impermeable but newly semi-permeable wall between them.
[8] According to Uffink, "... thermodynamic processes only take place after an external intervention on the system (such as: removing a partition, establishing thermal contact with a heat bath, pushing a piston, etc.).
The reason is that ordinary thermodynamic operations are conducted in total ignorance of the very kinds of microscopic information that is essential to the efforts of Maxwell's demon.
This may be brought about not by moving or changing separating walls around an unmoving body of working substance, but rather by moving a body of working substance to bring about exposure to a cyclic succession of unmoving unchanging walls.
This sets up the possibility of interaction between the two subsystems and between the composite system and its overall surroundings, for example by allowing contact through a wall with a particular kind of permeability.
[19][20][21][22] For a given such system Φ, scaled by the real number λ to yield a new one λΦ, a state function, X(.
As usual, these thermodynamic operations are conducted in total ignorance of the microscopic states of the systems.
More particularly, it is characteristic of macroscopic thermodynamics that the probability vanishes, that the splitting operation occurs at an instant when system S is in the kind of extreme transient microscopic state envisaged by the Poincaré recurrence argument.
For the third law, one statement is that no finite sequence of thermodynamic operations can bring a system to absolute zero temperature.