Gibbs-Helmholtz equation

Etymology
Named after Hermann von Helmholtz (who introduced it in an 1882 paper) and Josiah Willard Gibbs.

Proper noun

 * 1)  An equation for calculating changes in the Gibbs free energy of a system as a function of temperature: $$\left( \frac{\partial \left( \frac{G} {T} \right) } {\partial T} \right)_p = - \frac {H} {T^2},$$ where H is the enthalpy, T the absolute temperature and G the Gibbs free energy of the system, all at constant pressure p.