Laws of Thermodynamics

Empirical laws that explain the behavior of thermodynamic systems.

0th Law

Defines that temperature is equal for 2 systems in thermal equilibrium.

If 2 systems have the same temperature, then they are in thermal equilibrium.

If systems $A$ and $B$ are in thermal equilibrium then any system $C$ in thermal equilibrium with $A$ is also in thermal equilibrium with $B$.

3rd Law

As the absolute temperature approaches zero, the entropy of a system approaches a constant minimum value.

Establishes that it is impossible to reach absolute zero in a finite number of steps or processes. As a system approaches absolute zero, it becomes increasingly difficult to remove additional heat.

More of an interest in statistical mechanics; and not much in engineering.