ΔG°’ refers to a change in Gibbs Free Energy under “standard conditions”, meaning all concentrations are at 1.0 M, temperature is at 298.15 K (25°C or 77°F), and pressure is at 1.0 atm (1.01325 bar), just like ΔG°, but with the added parameter specifying a pH at 7.0 (proton concentration of 10^-7 M).

This value is important for several things in the study of stuff.

R is equal to the gas constant, which is defined as 8.315 J, which has to be divided by a thousand because G is in kJ, and the temperature is always at 298.15 K, so really, ΔG°’ = (8.315x10^-3) x 298.15K x ln K_eq, which means that ΔG°’ = -2.47911725 x ln K_eq.

ΔG°’ = -nFΔE°’

Positive & Negative

[-ΔG°’]	Negative Delta G nought prime — indicates a reaction is exergonic under “standard conditions”, meaning all concentrations are at 1.0 M, temperature is at 298.15 K (25°C or 77°F), and pressure is at 1.0 atm (1.01325 bar), just like ΔG°, but with the added parameter specifying a pH at 7.0 (proton concentration of 10-7 M).
[+ΔG°’]	Positive Delta G nought prime — indicates a reaction is endergonic under “standard conditions”, meaning all concentrations are at 1.0 M, temperature is at 298.15 K (25°C or 77°F), and pressure is at 1.0 atm (1.01325 bar), just like ΔG°, but with the added parameter specifying a pH at 7.0 (proton concentration of 10-7 M).

Related Concepts

[G]	Gibbs Free Energy —
[ΔG]	Delta G — a change in Gibbs Free Energy.
[ΔG°]	Delta G nought —
[ΔG°’]	Delta G nought prime —
[Keq]	Equilibrium Konstant —
[ΔH]	Delta H — a change in enthalpy.
[ΔS]	Delta S — a change in enthalpy.