Question

I have a question about gibbs free energy vs gibbs standard free energy.

We know that at equilibrium deltaG = 0 and Q = K, and deltaG standard is a non-zero value.
But I don't understand. If I want to see if a reaction is at equilibrium then I have to calculate the deltaG standard first, before I can calculate deltaG to see if its value is 0 or not.

And everytime I do that, the deltaG standard equals 0 under standard conditions. That dosen't makes sense comparing to the statement about that deltaG standard is a non-zero value at equilibrium.

Why is my deltaG standard always zero? The relationship between them will be: deltaG=deltaG standard at equilibrium????

Help me

Answer 1

• This question is related to Thermodynamics.
• The equilibrium for any reaction is indicated by the value of Gibbs free energy change.
• At equilibrium ΔG = 0 and it is called the equilibrium of spontaneity.
• ΔG = 0 means that the reaction rate is constant both for forward and backward reaction.
• Gibbs free energy is a measure of thermodynamic potential that how much reaction is left to do a net change and it is minimized when a system reaches up to chemical equilibrium. Therefore, whenever the free energy is zero, then the reaction is called at equilibrium and no more work is needed to be done. The derivatives with respect to the reaction coordinate of the system vanishes at the equilibrium point.
• Equilibrium does not mean that the equal concentrations. Equilibrium means that there is no net change in the whole reaction system and products and reactants are equally favored.
• ∆G is the change of Gibbs free energy for a system and ∆G° is the standard Gibbs energy change for a system under standard conditions that is at 1 atm pressure, 298 K temperature. ∆G tells about only the difference in the energy between reactants and products whereas ∆G° (standard Gibbs Free energy change) is unaffected by external factors and tells about the change the kinetics of the reaction.
• As the reaction moves towards forward reaction, the chemical reaction approaches equilibrium and ∆G becomes zero because the reaction is proceeding. whereas ∆G° remains the same because it is still referring the reaction when the reaction is at the standard conditions that's why standard free energy change is never be zero at equilibrium because standard temperature and pressure are always be present and due to this reason ∆G° is also referring the reaction with standard conditions.