delta G = delta G (STP) + R * T * ln(Q)

delta G: the change in free energy of a reaction

delta G (STP): the known change in free energy at standard temperature and pressure (25 degree celsius, 1 atm).

R: universal gas constant

T: absolute temperature

Q: reaction quotient

Since G is in joules/mole, T is in Kelvin, and Q is in ignored log units, the first expression of R (8.31451 J/mol*k) is used when the other quantities are in SI units.