loi thermodynamique

Overview

The laws of thermodynamics are fundamental principles governing energy, heat, and work in physical systems.

Key Formulas

Zeroth Law

$T_A = T_B \text{ and } T_B = T_C \Rightarrow T_A = T_C$

If two systems are each in thermal equilibrium with a third, they are in equilibrium with each other.

First Law

$\Delta U = Q - W$

Change in internal energy = heat added − work done by the system.

Second Law (Clausius)

$\Delta S \geq \frac{Q}{T}$

Entropy of an isolated system never decreases.

Third Law

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

Entropy approaches zero as temperature approaches absolute zero (perfect crystal).

Variables

Symbol	Description	Unit
$U$	Internal energy	J
$Q$	Heat added to system	J
$W$	Work done by system	J
$S$	Entropy	J/K
$T$	Absolute temperature	K

References

• Original Source