Temperature > 04 - Zeroth Law of Thermodynamics

Thermal equilibrium between material bodies is only achieved when they are at the same temperature. From this definition, the Zeroth Law of Thermodynamics can be concluded:

“If three systems are isolated from any other external universe, and two consecutive systems are in thermal equilibrium with the third, then the two consecutive systems will be in thermal equilibrium with each other”.

In order to fully understand the concept of the Zeroth Law of Thermodynamics, the definitions of: thermodynamic systems (open, closed and isolated), limited system and neighborhood must be clarified.

A thermodynamic system is open when it can exchange matter (mass) and energy (heat and work) with the environment; it is closed when it can only exchange energy, since the transit of matter is impeded by some obstruction; and, finally, a Thermodynamic system is isolated (adiabatic) when it does not exchange matter or energy with the environment.

A limited system, in this context, means the space up to which the experiment is delimited: forgetting everything else. And, the neighborhood would be exactly this “remainder”: the region outside the experiment.

In the three examples, the limited system would be the test tube containing a certain substance (where the study focuses), the neighborhood would be the space in which the tube is immersed (example: air).