# Standard Gibbs free energy equal to zero?

• Kqwert
In summary, when the standard Gibbs free energy (ΔG°) is equal to zero, it means that the Gibbs free energy of the reactants is the same as the Gibbs free energy of the products, indicating that the reaction is at equilibrium. This also implies that the equilibrium constant (K) is equal to 1. However, this only holds true if the initial amounts of reactants and products are equal. The ΔG° value does not have any other implications or deducible results.
Kqwert
Homework Statement
I have a question which asks:

What does it mean that deltaG_zero = 0?
Relevant Equations
.
At equilibrium, we know that deltaG = 0. But what about deltaG_zero, i.e. the standard Gibbs free energy? When is deltaG_zero = 0?

In the solution manual it says that it means that K = 1, but by calculating an equilibrium constant you are already stating that we are at equilibrium? I.e. that deltaG = 0, and K = 1 implies deltaG_zero = 0. A bit confused by this.

Kqwert said:
Problem Statement: I have a question which asks:

What does it mean that deltaG_zero = 0?
Relevant Equations: .

At equilibrium, we know that deltaG = 0. But what about deltaG_zero, i.e. the standard Gibbs free energy? When is deltaG_zero = 0?

In the solution manual it says that it means that K = 1, but by calculating an equilibrium constant you are already stating that we are at equilibrium? I.e. that deltaG = 0, and K = 1 implies deltaG_zero = 0. A bit confused by this.

You haven't said which textbook you're using, so it's not clear what the quantity ##K## is.

But also, when people use ##\Delta##, they usually mean the change in some quantity. So ##\Delta G_0 = 0## means no change in the value of ##G_0##. You're talking about change under what circumstances?

Kqwert said:
At equilibrium, we know that deltaG = 0. But what about deltaG_zero, i.e. the standard Gibbs free energy? When is deltaG_zero = 0?
I'm assuming that by ##\Delta G^0 ## you mean the standard Gibbs free energy of a reaction (since it is that that is related to the equilibrium constant ##K##).

##\Delta G^0 = 0## when the Gibbs free energy of the products is the same as the Gibbs free energy of the reactants. For a reaction of the kind
A + B ##\rightleftharpoons## C + D
##\Delta G^0 = 0## means that the Gibbs free energy of A + B is the same as C + D, so no side of the equation is favored, and at equilibrium there will be as much A and B as C and D (hence ##K=1##).

Kqwert said:
In the solution manual it says that it means that K = 1, but by calculating an equilibrium constant you are already stating that we are at equilibrium? I.e. that deltaG = 0, and K = 1 implies deltaG_zero = 0. A bit confused by this.
##K## and ##\Delta G^0## are constants for a given reaction. They give information about what will happen at equilibrium. ##\Delta G## tells you about a particular system, and can tell you if it is at equilibrium or not.

Last edited:
stevendaryl
DrClaude said:
For a reaction of the kind
A + B ##\rightleftharpoons## C + D
##\Delta G^0 = 0## means that the Gibbs free energy of A + B is the same as C + D, and at equilibrium there will be as much A and B as C and D (hence ##K=1##).
I don't think you really mean this. This will be the case only if you start out with equal amounts of A and B. For an ideal gas reaction, it means that the product of the partial pressures of A and B will be equal to the product of the partial pressures of C and D at equilibrium.

Chestermiller said:
I don't think you really mean this. This will be the case only if you start out with equal amounts of A and B. For an ideal gas reaction, it means that the product of the partial pressures of A and B will be equal to the product of the partial pressures of C and D at equilibrium.
You are of course correct. I had something in mind that I tried to express simply and it came out wrong

With K I mean the equilibrium constant.

I got a bit confused here.

what exactly does it mean that ##\Delta G^0 = 0##? Apart from it meaning that the Gibbs free energy of the products are the same as the Gibbs free energy of the reactants. Is there something more we can deduce from it?

Kqwert said:
With K I mean the equilibrium constant.

I got a bit confused here.

what exactly does it mean that ##\Delta G^0 = 0##? Apart from it meaning that the Gibbs free energy of the products are the same as the Gibbs free energy of the reactants. Is there something more we can deduce from it?
Are you asking for a physical interpretation (in terms of physical processing of the materials) for the standard change in free energy?

Chestermiller said:
Are you asking for a physical interpretation (in terms of physical processing of the materials) for the standard change in free energy?
No, I was wondering what other "results" one could take from ##\Delta G^0 = 0##

## What is the meaning of "Standard Gibbs free energy equal to zero"?

Standard Gibbs free energy equal to zero refers to a state in which a chemical reaction or process has reached equilibrium. This means that the rate of the forward reaction is equal to the rate of the reverse reaction, and there is no net change in the concentrations of reactants and products.

## How is the value of standard Gibbs free energy equal to zero determined?

The value of standard Gibbs free energy equal to zero is determined by measuring the free energy change of a reaction or process under standard conditions, which include a temperature of 298 K, a pressure of 1 bar, and a concentration of 1 mol/L for all species involved.

## What does it mean when the standard Gibbs free energy is equal to zero for a reaction?

When the standard Gibbs free energy is equal to zero for a reaction, it means that the reaction is at equilibrium and there is no tendency for the reaction to proceed in either the forward or reverse direction. This also means that the reaction is thermodynamically favorable, as the free energy change is equal to zero.

## Can the standard Gibbs free energy be equal to zero at any other conditions besides standard conditions?

Yes, the standard Gibbs free energy can be equal to zero at conditions other than standard conditions. However, these conditions must still be at equilibrium for the reaction, and the free energy change will be different from the value at standard conditions.

## What is the significance of a reaction having a standard Gibbs free energy equal to zero?

A reaction having a standard Gibbs free energy equal to zero means that the reaction is at equilibrium and will not spontaneously proceed in either direction. This information can be useful in predicting the direction in which a reaction will proceed, as well as the amount of energy that can be obtained or released by the reaction.

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