Laws of Thermodynamics

Empirical laws that explain the behavior of thermodynamic systems.

0th Law

If 2 systems: A, B are in thermal equilibrium then:

• They both have the same temperature
• Any system C in thermal equilibrium with A is also in thermal equilibrium with B

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

1st and 2nd laws are explained in detail in the next pages.

3rd Law

As the absolute temperature approaches zero, the entropy of a perfect crystal approaches a constant minimum value. For a perfect crystal, this minimum entropy is zero when the temperature is exactly absolute zero (0 K).

This law 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.

Mathematical Form

$$\lim_{T \to 0} S = S_0$$

Where:

• S is the entropy of the system
• S₀ is the minimum entropy value (typically zero for perfect crystals)
• T is the absolute temperature

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