Le Chatelier's principle

Le Chatelier's principle describes the stability of a system in thermodynamic equilibrium:

In response to small deviations away from equilibrium, the system will change in a manner that restores equilibrium.

This translates to conditions on the second derivatives of thermodynamic potentials such as entropy, $S(U,\ldots )$. For instance, the entropy is a concave function of its arguments such as internal energy. Thus, one has

${\frac {\partial ^{2}S}{\partial U^{2}}}\geq 0\ .$

Similarly, specific heats can be shown to be positive definite.

References

Related reading

• Denis J. Evans, Debra J. Searles, and Emil Mittag "Fluctuation theorem for Hamiltonian Systems: Le Chatelier’s principle", Physical Review E 63 051105 (2001)
• Pouria Dasmeh, Debra J. Searles, Davood Ajloo, Denis J. Evans, and Stephen R. Williams "On violations of Le Chatelier's principle for a temperature change in small systems observed for short times", Journal of Chemical Physics 131 214503 (2009)