Difference between ΔG = 0 and ΔG° = 0?

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

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

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Hannah Lee 2F
Posts: 117
Joined: Thu Jul 11, 2019 12:15 am

Difference between ΔG = 0 and ΔG° = 0?

At ΔG = 0, the reaction is in equilibrium. What is the difference between ΔG = 0 and ΔG° = 0?

Pegah Nasseri 1K
Posts: 100
Joined: Wed Feb 27, 2019 12:15 am

Re: Difference between ΔG = 0 and ΔG° = 0?

ΔG° is the change in gibbs free energy of formation, which is calculated using the equation ΔG°= -RTlnK. This is the gibbs free energy that occurs at equilibrium. ΔG takes into account ΔG°in its calculation: ΔG = ΔG°+ RTlnQ. Looking at the equation, just because ΔG°= 0, this doesn't necessarily mean that ΔG=0. The same is true for if ΔG=0, ΔG° doesn't necessary have to be 0. ΔG=0 just indicates that the reaction is at equilibrium while ΔG°= 0 shows that the equilibrium constant, K, is equal to 1 using the equation ΔG°= -RTnK = -RTln(1) = 0.

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