# ΔG° = –RT ln K

In equations, the following formula

$\Delta G^{\circ} = - RT \ln K \,$

is called “[name]” and states that the standard Gibbs free energy change ΔG° equals the negative of the product of the gas constant R times the absolute temperature of the system T times the natural logarithm ln of the equilibrium constant K.

History
The equation is said to have originated in the 1886 work of Danish physical chemist Jacobus van't Hoff and his so-called "van't Hoff equilibrium box"; although, to note, he derived the equation in terms of the chemical affinity work $w_A \,$, and never utilized the concept of free energy in his theories. [1]

References
1. Laidler, Keith. (1993). The World of Physical Chemistry (section: thermodynamics of electrochemical cells, pgs. 218-19). Oxford University Press.